What do you mean by design process? If you mean architectural decisions then the trading ones are quite complete (although some redesign may be worth considering), and remain the signer’s part and the user interface. It’s hard to evaluate a percentage, as it also depends on the choices made during the design process.
If you mean the whole development process then it’s almost impossible to say without the architectural decisions being made.
For example on the signer’s part, I think Jordan wanted to put it all inside the client, so that the B&C client of the signers would handle everything and talk to the asset clients. And Eleven briefly started working in that direction before the development paused. But I think it would be better to move all this signer code outside the B&C client. It would communicate with B&C and the assets through RPCs. These two directions are very different, and although their cost may be relatively similar it must be decided before being evaluated (or both could be evaluated but that takes more time in the design process). And regarding the user interface the range of possibilities is much larger (from a simple API to a whole exchange platform).
