I think 7-7.5 mil AAV is a great deal for a 25 year old #1 and the bruins shouldn't think twice about it, and I'd be fine with anything up to 8mil. Only goalies that make more then that are Bobrovsky, Vasilevsky, Hellebuyck, and Sorokin and all those guys have hardware/pedigree that Sway just doesn't (yet). So I don't think he can realistically ask for that unless he drags us to the cup and wins the conn smythe this playoffs, and assuming that doesn't happen and he still asks for that much you can still bridge him at a lower number since he's an RFA and tell him to go earn that big payday. But there's really no scenario where I'm trading Sway this summer, he is a golden ticket to another decade of stable goaltending.
For reference, the 8x7mil contract they signed Tuukka to in 2013 would be worth 9.5mil AAV next season going by cap %, and the two have extremely similar numbers through their age 25 seasons.