PIP support has been disappointing so far.
I found myself grumbling that it hasn't appeared in the Infuse Pro app, until I discovered in an Infuse support thread that it's largely down to Apple only allowing Apple supported video formats for PIP - so no mkv etc 🙁. I REALLY hope they relax that at some point, no way am I going back to the stunted, nay threadbare, functionality of the stock video player, uuurgh. I'd really like to make better use of PIP though.