Has anybody paid attention to were the car market is going. It's not 12v. The car manufactures are looking to 48v and AC. Now 12v isn't going to disappear anytime soon but you might find that the cool new boating toys will be AC powered sooner than you think.
I don't think that follows. The car market, particularly with EVs, is going to higher voltage DC (400V, 800V...) for pack voltage, but I don't see much AC other than accessory inverters, and not much 48V either. On the end use side, the trend is toward everything charged by USB (5V DC), and more and more efficient to maximize battery life for portable devices.
There are generally two classes of devices: things that use 100's to 1000's of Watts (water makers, electric cooking/heating, HVAC), and everything else. The everything else is getting more and more efficient, and will stay DC. Refrigeration is somewhere in the middle.
The higher power stuff is going to stay high power for the most part - you're not going to get USB powered HVAC or water makers.
If you want simple systems, you can go 12V only. In most cases it means HVAC is pretty much out, and you're cooking with propane and heating your water with diesel or waste engine heat.
But I don't need AC, actually prefer cooking with propane, and heating water with diesel seems a hell of a lot smarter than using diesel to run a combustion engine to spin a generator to push electrons through a resistor to heat water.
So as always it depends on the use case - but I AC aside I don't think you really have to give up much.
I am bald as a cueball though so I don't need a hairdryer. One could certainly do an inverter off batteries to power a couple of dedicated outlets for the few high power appliances that don't have great substitutes (hair dryer, microwave, toaster) - it erodes the simplicity thing, but it's still a lot simpler than a generator and a hell of a lot less noisy.