@swilliam - Stacks 3 should continue to be RapidWeaver 6 compatible for a while more. I think we will probably make the break at Stacks 3.5 next year sometime when we introduce some of the larger changes and API. Breaking from RW6 will allow us a bit more freedom to do a few things we couldn’t before with partials, images, and especially resources. 
So you’re good for a while more. But maybe keep an eye out for a good deal on the RW 7 upgrade. Did you see this post this morning?