Why would a miner want only half the network to build on their block?
That makes no sense... what is the +2hr timestamp miner trying to accomplish?
It would create a temporary fork and perhaps some confusion. Maybe even break some badly coded bitcoin applications if they do not handle forks well.
No, it really wouldn't, any more than a business-as-usual temporary blockchain race/fork creates confusion or breaks applications. Like the one-block fork we had
today.