I don't see why that would allow you to do anything less than what the NEC permits for dimensionally-equivalent listed conduit. If anything, I would be more conservative in fill and bonding requirements, in the unlikely event that I ever have to get away with using plumbing/fence pipe/fittings in a pinch.
Plumbing pipe is still metal, and thus still needs to be bonded if part of an electrical system. And it's not going to be any easier to pull that wire through it, since plumbing pipe interiors do not have the same finishes as listed conduit.
The whole key here is this is a sleeve for physical protection, not a complete raceway system - and because it isn't a racewaqy it is just a metal tubing - general raceway rules do not apply to it. Water pipe used for cable sleeve is no longer water pipe either - it is now a sleeve for wiring protection.
Because it is not a raceway system conductors installed in it need to be part of a cable assembly or other conductors that are not required to be installed in raceway methods.
The fact they are all effectively "bundled" where run in the sleeve means they likley will be subject to ampacity adjustments just like bundled cables run through bored holes in framing members are.
Conduit fill doesn't apply to a sleeve- but if that sleeve is long it may not be a bad idea to take it into consideration just to make the pull easier and avoid conductor/cable damage.
Bonding the sleeve isn't required but doesn't hurt anything either.