Or one could not use it at all.
As far as app support, you act as if iOS is some backwood platform without robust third party support.
I know perfectly well what iOS provides for IPC and it is insufficient for big-boy tasks. I mean, for real: are you going to throw a 16K image with 20-100 layers across heckin' x-callback-url every every time the user makes a change because you want to recompute a layer transform? Do you want it to come back before you die of old age? Or is it actually that, no, this isn't for for-realsies work, this is for the kind of dabbler who won't notice that, and for-realsies work should stay on a Mac until they kill it and we go back to Windows and Linux?
And please don't get me wrong: I'm acting as if the plugins that big-boy apps host are sometimes a decade old and are effectively out of support, because nothing in the Photoshop (or, indeed, most production) universe dies unless, well, Apple kills it. It's even more common for Office plugins and, as mentioned by another poster, it's literally more common than not for audio apps. (Gonna replace VSTs with x-callback-url? We binary-bolt this stuff together because a millisecond is a long time, remember...)