This has always been one of my “white whales” with async - where we can finally close the loop on rendering, as it were.
As it stands, I think we’d have to go in and overhaul the template engine to accomplish this; async functions, iterators and generators are different enough that they can’t really be slotted in, and the way templates render is especially difficult to work with in this context.
I’ve not been in that codebase in a while, but the first step would be having someone who knows templating somewhat well go and learn it and establish if there’s a core node render loop we can async-iterate over in a similar way to Jinja.