Call for feedback posted at en.wiki
I've posted a call for feedback on en.wiki here: https://w.wiki/35bt

I'd regard T277919 as a blocker.

Additional open tickets I'm aware of, I've given an indication of how I would prioritise them from an end-user perspective
T276510 Enable people to choose asterisk or colon for indentation on a per-comment basis (highest priority)
T265750 Make it easy to "outdent" by changing the colons/list level (high priority)
T278476 When there are long elements on the right side of the page, the Reply box opens after those elements, rather than instead of where the reply will be posted. (medium-high priority)
T278355 Discussion tools doesn't detect a manually-added signature when followed by any non-whitespace characters (medium priority)
T278357 Discussion tools should recognise three and five tilde signatures and add only the missing part (medium/low priority)
T263902 Enable Reply Tool to use context-specific indentation syntax (high priority if T276510 is unfixed, otherwise medium)
T279141 Discussion tools source more should display navigation popups when enabled (note I can't test this on the prototype as the gadget is not installed; medium priority)
T251633 Add support for extensions and templates within indented comments (low priority)
T275814 Cursor does not appear in Reply Tool's source mode (very low priority)

In T276614#6967801, @Thryduulf wrote:

T279141 Discussion tools source more should display navigation popups when enabled (note I can't test this on the prototype as the gadget is not installed; medium priority)

If you’re comfortable with the browser command line, you can load it with

mw.loader.load('https://en.wikipedia.org/w/load.php?modules=ext.gadget.Navigation_popups');

(It doesn’t work in DiscussionTools.)

I'd regard T277919 as a blocker.

Restricted task? I don’t have permission to see it.

In T276614#6971461, @Pelagic wrote:

I'd regard T277919 as a blocker.

Restricted task? I don’t have permission to see it.

T277919 is "Username suggestions (e.g. for mentions) should not include suppressed usernames". As is normal for tickets dealing with the potential leak of non-public information it is locked for security reasons (some user names have been suppressed for being libellous or containing personal information)

Thanks, @Thryduulf! I agree, I don’t need to see the details, the title is sufficient. Also understand why proper handling of suppressed names would high importance. I’m curious about how that all works under the hood, but I’ll be content with not knowing, to avoid another trip to the rhinologist for beans-removal. ;)

To the original question, “functions as they expect it to” ... my key expectation was that it works much like in the Visual mode, so yes, it does. Pasting formatted text and having the choice to convert the formatting to wikitext was pleasantly unexpected, since I don’t normally use NWE.

It’s a good list that Thryduulf supplied above, and several of the items are quite important to me too. (Particularly T265750, T276510, T278476 in that order.) But they’re not specific to the source toolbar, so might not prevent that being offered to people who already opted in to Discussion Tools?

In T276614#6967801, @Thryduulf wrote...

@Thryduulf + @Pelagic: the way you both have compiled, and in some cases, written tickets that represent the issues you've observed leads us to better understand how you are thinking about the tool and prioritize improvements to it. We appreciate the time and effort you've put into this!

A couple of clarifying questions...

@Thryduulf:

• Of the tickets you listed in T276614#6967801, would it be accurate for me to understand T277919 as the ticket that is directly related to the DiscussionTools's new source mode being made available as an opt-in beta feature? I ask this thinking something similar to what @Pelagic shared in T276614#6972687.
• Of the remaining tickets you listed in T276614#6967801 [i], would it be accurate for me to understand you as prioritizing them in the context of the Reply Tool being offered as an opt-out feature at en.wiki? See: T279397.

i. T276510, T265750, T278476, T278355, T278357, T263902, T279141, T251633, T275814

In T276614#6972687, @Pelagic wrote:

To the original question, “functions as they expect it to” ... my key expectation was that it works much like in the Visual mode, so yes, it does. Pasting formatted text and having the choice to convert the formatting to wikitext was pleasantly unexpected, since I don’t normally use NWE.

Wonderful – thank you for confirming this, @Pelagic.

It’s a good list that Thryduulf supplied above, and several of the items are quite important to me too. (Particularly T265750, T276510, T278476 in that order.) But they’re not specific to the source toolbar, so might not prevent that being offered to people who already opted in to Discussion Tools?

Understood. Similar to the question I posed above, are you raising T265750, T276510, and T278476 in the context of a particular milestone (e.g. offering the Reply Tool to everyone at en.wiki as an opt-out preference)? Are you raising these in the context of, "These are the issues I've encountered that impact me" Something else?

If I've understood your question correctly, I would say that T277919 should be resolved before a version of discussion tools featuring pinging with username suggestions is offered as an opt-in or opt-out feature.
T276510 should definitely be fixed before DiscussionTools is offered as an opt-out feature, with a strong preference for fixing it before offering it opt-in.
T265750 is not a blocker for an opt-in feature but should be fixed before offering it as opt-out one.
The other tickets are not blockers for either milestone, but fixing those I've listed as medium priority or higher before making it opt out will improve the reception.

I've just created T279424 Abandoned comments get resurrected (unsaved changes). This is a medium-low priority task which can be fixed before or after DiscussionTools becomes an opt-in feature.

I've just discovered the existence of T279400 Make the feedback link for New Discussion tool point to the project page about the New Discussion tool (not the Reply tool)
It would be desirable, but not essential, to fix this before rolling out further.

T277919 has now been marked as invalid, but the problem remains. It seems T25310: Global suppression does not work properly when the target has already been locally blocked seems to be the relevant task for that, but that's been open since 2010 and is marked as low priority, with two blocking tasks also marked as low priority. As the issue is still (imo) a blocker it might be worth considering whether it is possible/desirable to release a version of DiscussionTools that does not include username suggestions.

@Thryduulf: this additional context is helpful. I've related the tickets you drew attention to the Reply Tool being offered as opt-out feature at en.wiki by adding them as sub-tasks to T279397.

In doing the above, I am not indicating that we are committing to resolving all of these issues. Tho, I am committing to us all talking about them again, likely on-wiki, when we start talking about offering the Reply Tool as an opt-out setting. [i]

i. I hope the above didn't come across in any kind of negative way; I just wanted to make sure what I was communicating was as clear as possible ^ _ ^