I highly doubt that BSM will be allowed after 1.7.
This is the Survival Games. You're supposed to survive, and it isn't supposed to be easy.
BSM makes surviving much easier.
Now, MCSG won't demand that players don't use the vanilla sprint key. That does make it easier, but it won't make it as easy as with BSM. I don't know if this makes sense - It's a jumbled general thought in my head, and I'm probably explaining it wrong.
Let me put it like this:
BSM - 1
1.7 Sprint Key - 5
1.6 and before - 10
The higher the number, the harder it is to survive. (Based solely on sprinting. Surviving isn't only sprinting.) With the new sprint key, it's a lot easier, but with BSM its insanely easy.
"Why not remove the sprint key for MCSG?"
A) Tough to do - The Devs do a ton of coding as it is. This would just make a lot more work for them. My guess is that removing a vanilla feature is really difficult.
B) It would make people leave MCSG. Yeah, many of us Forumers don't like it. But what about the average noob, which makes up more than 75% of the players on MCSG? A huge amount of players would leave MCSG for other servers that kept it.
C) Why would you want to remove a Minecraft feature? The makers of Minecraft listen to the community, and the community in general wanted a sprinting feature.