is any progress or even discussion in this area? 

I don't insist on any specific solution, but this is becoming a real issue as hardware wallets are more widespread. I'm sitting next to TREZOR for 40 minutes already, because it streams and validate some complex transaction. By using proposed solution, such signature would be a matter of few seconds.

That's also not just about time/resource/hw cost optimization. I'm talking about possibility of huge simplification of the firmware (=security FTW), because 50% of actual codebase is solving this particular downside of Bitcoin protocol.

So, there's real world problem. On which solution can we as a community find a wide agreement?

Best,

Marek