A fine, but expensive and mechanically complex solution. Dual boiler machines generally cost thousands even for small home machines. Commercial dual boiler machines will set you back at least $10-30k, easily.
Besides that, there's the warm up time. Often 30+ minutes on a commercial machine, then the electricity cost of keeping several litres of water and heavy blocks of metal at boiling point too.
It's high time espresso machines got a mechanicals simpler, cheaper, more environmentally friendly update. On the home front, Breville and Decent are doing this, while commercially I think some Ascaso machines use the same tech as Decent (not 100% sure on that though and when I reached out to them about it when considering one of their machines they just told me "work with your local dealer". There's exactly one Ascaso dealer in the country and they don't speak English so that wasn't much help).
Not to dismiss dual boilers or even good heat exchangers. Both of them are beautiful technological designs. But they basically haven't changed since the sixties.