I think I'll be ok with the boot size, since I'll keep my S, but if they had a Model 3 wagon, I'd prefer that.
I also don't think it really helps just looking at cu/ft of storage space. The layout is also important. I'd rather have a boot that's wide and deep, than high, like in a traditional hatchback. Deep, wide and high one the other hand... Let's hope Europe puts enough pressure on Tesla. The deviation from a sedan to a wagon isn't too big and the losses in efficiency are small, compared to a CUV.
Sadly Americans don't like wagons and since Tesla is an American company, with the US being their biggest market (so far?), I see little chance for a wagon.