I am not going to say that an individual block time shall be perfectly valid. The only restriction that the top of a main chain shall not end in remote future.
This is just the problem, "remote future" is effectively undefined because "current time" which it is relative to is effectively undefined. The allowed values for "remote future" would have to be quite remote, and quite broad. As such, I don't feel that this would accomplish what you think.
BitCoin is also using time paradigm to calculate thresholds. And it is also possible in bitcoin to form a huge chain pointing to the future and this chain will be declined because it is pointing to the future. The difference is not very big when we talk about the last block only. If some crazy miner will ignore this and will keep mining based on a block from the future he will finally end up with short chain when time will catch it up. This is not efficient all the gamers will try to use most recent blocks. Like in BitCoin.