This feature has been developed.

The seed phrase for the first ID of a Keychat user is also the seed phrase forecash, which can be used to backup ecash, just like the seed phrase of an onchainn wallet.

nostr:note103pekl3q5wh275dw0zlqwgec2qy7lkp9d7xsk7nuy926xl9805lsj3w6ua nostr:note1cf906evj64t0rdxt7wn983r5t8cur7re5e2tq6yuwa7ggz05sg6qnjwrl6