"Transaction identification by prefix: this feature will let us to cut off ring signatures from blockchain that under checkpoint - save space by 30-70%(depends of mixin usage)"
has already been implemented, it's all reasons for people to leave bitcoin.
It is.
Actually it was not a big deal to implement: just change get_transaction_id function (make this function use only tx prefix data) and change transaction serialization map (i've never liked bytecoin mess in ring signatures serialization) to let transaction load itself from blob without ring signatures. Now transactions included into merkle tree only with tx prefix data.
But, to avoid misunderstanding, i want to make clear that this issue is not related with UTXO(as some people thought).
It's just an improvement of bytecoin, that have tonns of ring signatures, that actually not used after transaction lay down in blockchain.