Bottom line is the bottom line.... companies do what is best for them.
If that means being the un-carrier and more open to consumers desires to be free, that might be how T-Mobile stays. If it means locking in customers and following AT&T and Verizon in making it hardish to switch to another carrier...
For now T-Mobile isn't a factor to me, other than as a National pressure point to keep Verizon in check. But it they get around to actually adding more towers.....