are you recommending #9901

Nope, that just adds some specific class for chosen, what I am suggesting is to totally remove from core all instances

JHtml::_('formbehavior.chosen');

Some additional work will be needed for tags and maybe some other scripts that expect chosen to be loaded

What specific a11y issues

Found this harvesthq/chosen#264

try the simplest test:
move around in a page with tab till you get to a (chosen) dropdown, then try to use keys to navigate inside the selected (chosen) dropdown. Try se same test in a page without chosen. Yeah it's that bad...

didnt seem too bad to me - tested with the category list on a new item

I also didn't found problem with lists - but I guess we don't see it as we should.

But found issue with popup window edit module settings at module assignment tab in menu item. - can't be closed to cancel or to accept changes (especially in module assignment window).

I don't use Joomla, but I have been auditing a whole bunch of great accessibility enhancements in a fork of the "chosen" plugin - can be found at https://github.com/cooperfellows/chosen/tree/a11y-updates

See the conversation towards the end of harvesthq/chosen#264

If it wasn't for this forked version I would be recommending that we also did not use the plugin in the project.

Hi - I am closing this here. Please create an issue directly to the a11y group here https://github.com/joomla-projects/accessibility/issues