I actually think I remember reading some Metrolinx document where they conceptually mention the idea of using Summerhill as a midtown GO station at some point in the future. Aside from the density issues, I think we really need to address the rail corridor first as that can have a huge impact on future transit plans.
Here's a thought. If it were feasible to cover that portion of the rail corridor with a 'roof', like they partially did on the north end of the Rogers Centre (for the hotels vehicle drop off area), do you think that would in any way change the need for the 30m buffer? I know it probably won't address any of the concerns about future expansion, but it may address some of the concerns of noise, nuissance, and safety for those who may end up living on the north side of one of those towers?