I had very similar ideas :)
I agree that cutscenes would be cool. I'm unsure about the exact implementation for now.
Regarding custom elements - by "softlocking" you mean that they are limited to 18 elements? I'm planning to make a pagination and allow an infinite amount of elements too.
You can change border tiles by selecting "edge blocks" in the draw section dropdown.
And i also agree that more VFX and maybe some sort of VFX editor would be nice and make PP flashier..