Basically it would be nice to allow to add special characters to gallery tag like |, En dash, ... and others, which are needed if we'd like to be typographically correct.
|Resolved||None||T87532 Allow to add special characters to gallery|
|Resolved||None||T137286 Provide a full rich-text editing and options setting for <gallery>s in the visual editor|
|Resolved||Arlolra||T110910 Implement <gallery> extension natively inside Parsoid|
|Resolved||Arlolra||T55874 Add a generic extension registration mechanism|
This is possible these days, both the main gallery caption and individual image captions support the full set of editing features (with the limitation that they may only be a single line – so no headings, lists, tables, etc.).
This was mostly implemented in rEVED12cc56400b4e: Make gallery dialog work with native gallery implementation (merged in March 2018).