In today's NE Alliance press release, B6 mentions that starting this fall, they'll be running a split operation at LGA between MAT and Terminal B, with all operations to be eventually consolidated at B. I'd imagine the full move will be dependent on when the new concourse is finally finished and all gates open. It'll be interesting to see what routes (i.e. the more leisure focused or the more business focused ones) they keep at MAT vs. Terminal B.
This is a nightmare. MAT saves me dozens of minutes with all the construction and traffic and time to get an Uber at terminal B. This won't be any better in the fall. If I have to fly another airline I literally fly into JFK just to avoid all that.