Yep. Water mitigation + 1.5% max RR grades making the inclines up/down super long in length. The total project area would have to dramatically increase in size because of the distended inclines, and that chews extra $$$ like a drunken sailor. Not only for the extra complexity of tunnel cuts & waterproofing, but all the extra linear acres of surveying/permitting/etc. over larger total project area, which serve little functional purpose except chewing more time and resources in paper busywork. Plus, watch BU start inserting itself into the mix as a pot-stirring political entity of greater consequence the closer that rail incline gets to the Comm Ave. overpass. They don't really have a ton to say about the 'throat' so long as that fight is all to their backs behind the Agganis Arena loading dock with their retaining wall to the tracks being untouched by it all. Different story altogether when you're popping headache meds at their unsolicited "Why don't we try building a midair-suspended back porch off the CFA building over your lovely new tunnel incline?" renders.You could do Green GJ but not CR.
Right now, mercifully, BU isn't all that featured a player until the 'throat' stuff is done and it's back to troubleshooting the nonsensical street layout over the slab and the inverted West Station positioning that's inexplicably isolating from their campus.