max reorg depth in NXT is 720 blocks
Checkpoints are centralization.
For a centralized coin, then anything works, you don't even need PoS nor PoW (except to fool people with).
If we don't have decentralization, then the entire plot has been lost.
Do you need an example? Here you go (remember the Chinese mining cartel allegedly controls 65% of the Bitcoin hashrate):
https://www.reddit.com/r/btc/comments/48nnaw/the_truth_comes_out_core_devs_have_convinced/