Apparently Bulletproofs can reduce the average tx from 15kb to something like 1.5kb-3kb which is still slightly larger than Bitcoin's 0.5kb but definitely a significant improvement. Would something like RuffCT/StringCT reduce that even more?
As currently envisioned that would increase the ring size (so better privacy) without increasing the TX size but wouldn't significantly reduce the tx size. There might be other methods/improvments developed in the future, who knows.
I'm also curious if we would be able to prune the blockchain in the future, like Aeon or Boolberry do - although Monero can't use the same method IIRC.
Some pruning (about 80% IIRC) is already partially implemented and will be rolled out when it is ready.