I'd be surprised to see them over at BCH, BMC, and MGH because those hospitals are major teaching sites for BU and HMS - their first priority will be accommodating students from those schools. St. E's is switching their affiliation from Tufts -> BU as of last year.
Since they already rotate through Barbara Bush/Maine Medical, I'm not sure how much extra capacity they will have there beyond the 20-30ish folks per year who are on the Maine track.
Big question mark for Lahey/SSH, though I'd be surprised to see a dramatic expansion from them given that it seems like the reason for the Tufts/Floating hospital closure was because of low reimbursement for peds care.
I feel bad for the folks at Tufts. The children's hospital there was a great institution, and it is a real ****ty move to the faculty, staff, nurses, patients and especially the residents and fellows, to close so suddenly.