Canada

Those are all serious concerns, and I expect PHEV vehicle design to change over the next few years (my only concern is how many "few" is).

The more sensible design if you're are going for 'ICE as backup', not 'electric as efficiency improvement on top of ICE' is a typical electric 'drivetrain' and battery, with a generator, more similar to diesel-electric trains. A switch to diesel in general wouldn't be a bad idea either, but the north american market would be resistant.

Depending on how gas prices and the EV market go, I wouldn't be surprised if drop-in engine replacements for converting ICE vehicles to hybrid become easily available in the next 5-10 years either, especially on larger vehicles.

It'll still be a typical ICE transmission, which will still be less efficient, but you can run the engine at the ideal RPM all the time which helps make up for that. Where to put enough battery to be worthwhile is problematic, but the vehicles that would benefit most tend to have vestigial truck beds, so there is that