The whole idea of a coin is as a currency...did you forget? Changing block confirmations to 6-12 hours makes it impossible to use NYAN to buy anything...What if you wanted to buy a coffee but it took 6 hours just to confirm your credit card? That long of a block time defeats the whole point of crypto.
That aside, the reason we can't afford to lower block rewards with X11 is because however much we lower it is however much less miners we will have. Lets say block rewards become 10% of what they are now. Then we will have ~10 Mh/s as our network hashrate. Well guess what? I myself have roughly 9 Mh/s under my control. I would then be able to go in and kill the coin with a 51% whenever I wanted to. Is that a vulnerability you want the coin to have?
POS will not suffer this problem since anybody can just open up their wallet and leave it open. Therefore, many more people will be able to hold NYAN and protect the network. It also costs very little from an electricity point of view to do so. Miners have obligations to meet, they won't stick around in our network providing hashes to protect us just for fun.
Even with the 120 block maturity, my nyancoin are sent from wallet to wallet and usable within 3-10 minutes. New block maturity does not have a significant effect on the usability of the coins. This is a long held misconception. Doge is at 4 hours right now.
How does lowering reward magically lower hashrate? What lowers hashrate is less miners.
So I need to open my wallet and leave it running to collect coins with PoS? Talk about ass pain favoring bagholders, with possibly corruption by said people when most dont want to leave a wallet with a few thousnd nyan open on a pc 24/7 only to make nearly jack shit returns.