Most fighting fighting games function just fine with teleportation moves, even with the back-to-block. If they were really problematic, they would no longer be in fighting games that don't have a block button.
Depends on the teleport. Something like Dhalsim or Raiden is fine.
something like Smoke's forces people to commit to walking forward and possibly eating a combo at anytime just to avoid a teleport if it's been conditioned.
They could have crossups in MK10 w/o having to remove the block button.