It only needs 55% to be activated early. It activates no matter what, even if miners don't signal. It probably would be better for the health of the ecosystem if it isn't a miner activated softfork (we don't want miner centralization even for good soft forks). If it doesn't get the 55% miners to signal then it will be a user activated soft fork. Right now ~15% of nodes (similar to bip 148) are running RDTS. That means a significant portion of the network will not accept blocks with arbitrary data. This incentivizes miners to respect the rules of node runners.