https://www.somervillema.gov/departments/union-square-planning has all the documents, including the recently-updated massive full proposal document.

If you don't have time to read 250odd pages of development planning, just look at pages 12-13, 22, and 25. That's the list of which sites are in the proposal and some maps of what they're planning on doing.

The plan is expected to take at least 10 years, and will go in phases, so it's not like they're going to raze the whole thing at once.