I can tell you how I see it from my point of view. I think the first step is to get Blaze to be available as a NPM module. And split also dependencies into separate repositories/NPM packages.
Then having working testing. And some stand-alone documentation page. So first we should have basic project infrastructure.
After that I think it should mostly depend on the community, what would they like to make pull requests for.
As a matter of fact, I do not think I will have much time to work on Blaze myself. I made Blaze Components work pretty well for me and I think that Blaze should mostly now be in maintenance mode, fixing some long standing issues, but should be kept backwards compatible. On the other hand, if there are some backwards compatible changes needed to make new stuff on top of Blaze work, that would also be OK from my point of view. If community would like, we could try to get Blaze Components to be Blaze 2 or something, a new version, but I personally will not be pushing for that. It does not feel right.
I think one interesting next step would be server-side rendering. I tried to play a bit with that and it seems to work well.
One thing I would like to see for Blaze (especially with components) is some type of gallery. Something like I made for Blaze Components: http://components-explorer.meteorapp.com/ (Site is going down all the time, since I migrated it to Galaxy, 
) So a more visual way to navigate Blaze packages.