Redmine

+1
Would definitely need this.
We have several new teams creating new projects, they would prefer other wiki syntaxes, at least I would like to show them the Redcarpet plugin.. But since I can only switch over globally, this would break all existing project wikies.

Ideal would if Redmine remembered, the syntax for each entry (maybe at issue/wiki level) and at least don't change that by the global settings. This would allow local experiments without break everything.
Some neat pragma would probably do it - my 2 cents.

Related to #8095

Also related to #15520, for a per-project setting to work, there will also need to be a global one for home-page blurbs, etc.