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.
Temporary forks happen every day (they are often called "orphan" blocks). Every time two miners (or pools) solve a block at close to the same time, some of the network hears about one block first, while some of the network hears about the other block first. Bitcoin is designed to work this way, and to adapt properly to the longest fork once another block is found.
Any "badly coded bitcoin applications" are already broken if they don't handle this daily occurrence properly.