Well I think you said it, possibly lot of work for Scintilla for little return. But you can always ask, but don't be surprised or upset if its no. If Scintilla provides an option then "somebody" can make a PR to add it to Geany.
But the general approach these days is to make more features asynchronous, like Language Servers, they can be slow, so freezing is unacceptable, and when they return their output a while later it might mean re-wrapping if they cause changes to the display which makes more freezing. So in general any freezing is frowned on.
developers of big software don't like a freezing behavior because it is a break in the flow, and the flow seems to be holy.
Not so much the developers as the users, who kick up an un-holy ;-) racket if things freeze.