Ah, now I just found this link to another thread underneath the “Read this first” post: Is there a list of upcoming/planned features?
It seems the OP of that thread asked the same question as me in February. There weren’t many replies to his thread, so my feeling is that local editing is not something we can expect anytime soon. It would still be nice to know if implementing local editing would be a major undertaking, like a complete rewrite, or whether it’s a doable task. I believe it’s a feature many are looking for, so it would be nice to know if it is something that is realistic to wish for and to implement 
And yes, I am aware that round-tripping to Gimp is possible