PHEV for future proof is good point. Simple plug cost could be minor, but HEVs have small battery (and don't use fully for long life) so just adding plug is almost useless. Who wants only 5km EV range?
that's a lot of my point. The Prius prime (for example) has a 8.8kwh battery, which at $130 per kwh works out to $1150 of battery. That's not negligible, but the benefit is pretty massive. That's a big enough battery to get you 20-25 miles of pure electric range which means that if you have a short commute, you will dramatically cut your gas usage. Full BEV is great obviously, but IMO, you probably want 1 car to be gas optional still, and a PHEV gives you an easy path to be driving almost 100% electric with 0 compromises compared to a gas car.