Monero has already made substantial changes to its codebase. Will the RingCT fork make it harder for other CryptoNote coins to merge improvements made to Monero?

Does every major fork make it more difficult for downstream Monero forks (like Aeon) to merge improvements made to Monero (such as LMDB now and soon RingCT)?

Will upstream merges (such as pruning or PoW changes made by Aeon) become more difficult for Monero to implement in the future as its codebase becomes more and more different?