Regardless of what the user chooses, this should use the same as the preceding comment for all except the final character. e.g. in the sequence:
Comment1
:Comment2
::Comment3

The tool should output either
:::Comment 3 or
::*Comment 3

replies to that should be:
::::Comment 4 or
::**Comment 4

etc.

Hello, I have a question as an editor, English Wikipedia says:

In https://en.wikipedia.org/wiki/Wikipedia:Manual_of_Style/Accessibility#Indentation:

A colon (:) at the start of a line marks that line in the MediaWiki parser as the <dd> part of an HTML description list (<dl>).

In the same source:

The result is that assistive technology, such as screen readers, will announce a description list that does not exist, which is confusing for any visitor unused to Wikipedia's broken markup. This is not ideal for accessibility, semantics, or reuse, but is currently commonly used, despite the problems it causes for users of screen readers.

Then, will the colon option be deprecated in the future?

T276510#7736168: ppelberg removed a parent task: T279397: Deploy the Reply Tool as an opt-out preference at en.wiki.

Rationale for removing this ticket as blocking the en.wiki Reply Tool opt-out deployment: this ticket is a request for new functionality within the Reply Tool which people can currently use the existing source editor to achieve.