This is depended on by many other tasks and has had at least two WMF CUs be a task they'd like seen to be taken on in a recent discussion on checkuser-l. I'm looking into this.
Will be in the next train.
Patch merged that fixes the link. If a different link is wanted the parent task can be used to discuss them in general.
Sat, Jun 25
One concern I have about that is bullseye currently requires a login to see the information. This means that third-party wikis probably won't have access to some, if not all, the information. Perhaps limited info about the IP (such as not spur or any other service that has a limit) can be shown to those not logged in. Making the different tools into one link would certainly be nicer in terms of UX and easier to use.
Any update from Anti-Harrassment as to whether they would take this on (@Niharika)? Just don't want to trample on your current work if it's being worked on / going to be soon.
Used core's ListToggle class that is used for suppressors. Works well and does not interfere with the checkuserblock form (i.e. pressing the options does not effect the checkboxes in the checkuserblock form).
This implemented in core for users with the suppress right on Special:History. Perhaps this could be ported over.
In theory Special:Investigate's "IPs & User agents" table could be used to make the design clearer. The current system of bullet points with two nested lists isn't really ideal. Using headers for each user would add lots of extra content. A table seems most idea and in theory the code from Special:Investigate could be reused?
Triaging as Medium as parent tasks which are blocked by this being implemented are also medium.
Patch has received a +2 so will be merged in. It should make the next train.
Thanks for the nomination.
Fri, Jun 24
In the mean time we could make it so that this link does not show up for anons as anons can never be check users.
Although this was the older task, T249562 is where the patches that fixed this referenced and that was closed first.