Nothing stop you to start mining now and also like you suggest if miners wait to mine coins for higher reward it will dump the price.
Really something to consider
longer PoW = more dump = better coin distribution. People who cant mine buy coin from miner dump at cheap price which better distribute the coin. As a miner of course they want to cut as soon as possible but as an investor they want as cheap coin as possible.
Longer PoW better distribution for miner (more miner when PoW reward get higher) as well as investor get cheap coin.
Personally in favor of this idea, I am worried PoW finish, PoS start at 15k, chance might happen the block chain stale at 15k, that is teh reason most coins have pos start before pow end.