Others probably could answer this more analytically but I don’t really see the benefit there. You’re gonna lose time tracking across the square (yes, only a little time, but the journey from Washington up to the station has many ped crossings and is slow), and you’re gonna skip the last leg that actually gets a lot of ridership in my experience (and is a lower income district anyway) — South, Archdale, all those stops). It just doesn’t really seem worth it to me.If Needham went full Orange (and Green on the other end), wouldn't there be enough room in the ROW to fit essentially a "return" bus route to Forest Hills? So buses could drop off at Rozzie Square OL station, then entire this bus lane in the ROW and go direct/express to Forest Hill skipping Washington St (and keeping passengers). Once at Forest Hill they could go back out normal routes and down Washington St if needed (for those not just starting/terminating at the Square).
I think the benefit is mostly to the west roxbury riders, coming in on the 37 and other lines and passing by the commuter rail station anyway via Corinth/South/Belgrade. And of course a full OL conversation probably leads to some ppl on those routes getting off sooner at the W Rox commuter rail stations if those are now OL.
Last aspect is of course let’s not forget that removing needham line frees up more space on the SWC to beef up frequencies on the other purple lines, which could serve among other people some folks who’d otherwise be on the 34E from Walpole and Norwood.