We need to take a step back and address the innertube things properly. Just using two existing tubes or 4 , or whatever, doesn't necessarily improve things ..
I'm proposing a none circular tube ! The Sausage !!
A Sausage should conform to the international sausage standard 20cm length.
For a 27.5 wheel, you'll need 10 standard Sausages and 10 valve holes. For a 29er you'll need 11 standard Sausages and 11 valve holes - lets not worry about spokes ...
Obviously being the bike industry, everyone will rush to develop their own proprietary Sausage standard purely to make everyone's life difficult.
The great thing with the Sausage is that anyone can carry a pack of Sausages as they're light and take up hardly any space. Four Sausages and you're covered for 4 punctures !
The other great thing with the Sausage is that you don't have to remove the wheel to change a Sausage - even more ideal for hub motored bikes. Just find your limp sausage by feeling round your rim, or have a friend feel round your rim and see if they can find your limp Sausage.
Swap out your Sausage, add a tiny bit of air - which takes seconds, and you're off !! Mere seconds for a trailside flat.
Another advantage of the Sausage system is that you can most likely continue even if you lose one or two Sausages until you're at the bottom of your run. OK, performance will degrade slightly, but you should get away with it.
Most people will probably also elect to run the Slime Sausage, though if you're a major Sausage gobbler, you'd probably be better switching to tubeless.