I can help in fixing things and also it would be good to have it on a RTL wiki.
|Resolved||ssastry||T175706 Progressively switch Wikimedia wikis from Tidy to RemexHTML|
|Resolved||Jdforrester-WMF||T176150 Enable RemexHTML on fawiki|
https://fa.wikipedia.org/wiki/%D9%88%DB%8C%DA%98%D9%87:LintErrors shows that there are over a thousand high-priority errors. I thought that these needed to be fixed before a wiki changes from Tidy to Remex. The comment from @Jdforrester-WMF in T175971#3609583 – as well as the descriptions in T175971, T175972 and T176088 – seem to suggest that.
It's a sufficient but not necessary condition. If a wiki is already unaffected by the change we'll make it earlier than other wikis, so subsequent edits don't introduce new issues.
If a wiki has some Tidy-relevant errors (the "high priority" section), then the content display will change on those wikis after we throw the switch – but the local community can go and fix those pretty easily, and in some ways it's easier to ensure that you've fixed them as you can see the results.
I'm happy for us to proceed if @Ladsgroup is – it's him, not me, that has the ability to fix these working with the local editing community, after all. :-)