You can do almost everything on that Contracts page without needing transaction replacement. Lock time does work today (as of Dec 2013), transactions with lock_time can't go into the blockchain until the time is reached.
Transaction Replacement is not supported because the developers have said that the whole idea of nSequence-based replacement is problematic, and may never be enabled apparently it causes potential denial of service problems. They discuss it here:
However, I don't think transaction replacement is really needed because sometime recently the developers made so transactions using lock_time and version < UINT_MAX are "non-standard". What this means is that transactions using lock_time won't be relayed on the peer-to-peer network until the lock_time is reached, at which point you can push the transaction for relaying and it will be considered standard and able to go into the blockchain.
The reason I think this takes care of most use cases is because replacement was only needed when the locked transactions were being relayed, and stored in the memory pools, so if a transaction came along that wasn't locked, it wouldn't be accepted because replacement wasn't implemented, and the locked transaction was already in the mempool. Since the locked transactions won't relay and store in the mempools now until lock_time is reached, I believe replacement is far less important, so the fact that it doesn't look like it will be implemented anytime soon is not a problem.