Isn’t signing the evm-transaction part of Assigned: ICDevs.org Bounty #27a - NoKeyWallet - Motoko - up to $10k?
I’ve already implemented it in my Motoko library - ic_no_key_wallet.mo/src/lib/NoKeyWalletLib.mo at 474808c71ee7d275771a99c2df0d022d16430a8b · darkdrag00nv2/ic_no_key_wallet.mo · GitHub. It is very close to completion and only e2e testing is remaining.
That being said, it makes inter-canister calls to the evm-utility library for encoding/decoding/hashing as per your suggestion here. If we’re trying to avoid inter-canister calls, then it might make sense to implement it here in pure Motoko.
Otherwise @v1ctor can just use my library to sign the evm-transactions which will make async inter-canister call. May be I am missing something here 