Apologies in advance if this is me being slow, but I just tried copying a bunch of stacks from Rapidweaver and pasting them into Stacks 6, beta 66. More from sheer optimism than anything else, because I only tried this the other day and it definitely didn‘t work. But… did this really just happen? They copied and pasted and… work!
IDBI! IFDBI!
Isaiah, 
Same stacks are installed in both applications, of course.
Sorry if I seem a bit manic, but this is the most exciting moment in the Stacks world since before Covid. I now discover it‘s possible to drag and drop items from the Rapidweaver Stacks ‘Resources‘ window into Stacks 6 — for instance, to drag an image from Resources straight into a Stacks 6 stack‘s image well.
No doubt there are some beta bugs in all of this (although I‘ve not hit anything yet). But migrating sites is on!