I've enabled post quoting on infosec.exchange, infosec.space, and convo.casa. On the web interface, the boost icon will now bring up a small menu that will let you either boost or quote. You can only quote posts that the author has granted permission to, and since this is a new feature, there probably won't be too many.
Reminder that most other fedi-software allows quote posting without the mastodon-style consent, as does most mastodon mobile apps, so be aware of that.