Probably the biggest issue with AR10 style rifles is there is no mil spec for them like the AR15. Your choice of platform may/will lock you into a parts/upgrade path.
I don't know about that. maybe 5 yrs ago, that was a very valid statement, still true that there's no MIL-spec, yeah, maybe SR-25, however the AR-10 industry seems to be coalescing about 2 de-facto formats:
- Armalite AR-10
- LR-308 DPMS-high
maybe in 5 more years, we'll see the outcome of the VHS-Betamax shootout, or maybe it'll always be Ford-Chevy, but for today, those are pretty much defacto almost-standards, pretty well supported, parts conformity.
but you still have those freak-flags, those independent outliers, that have decided to forge ahead with their own unique formats: e.g. PSA, SIG 716i, with their own insidious proprietary aspects, moreso than the afore-mentioned 2 formats.
it's still good practice to not mix-n-match upper and lower receivers, but as far as barrels, rails, rail-heights, charging handles, BCGs, it's jelled pretty much. it's like cook-book, but with many recipes. or maybe a magic book of potions, and you can't substitute eye-of-newt for toe-of-frog, otherwise your bolt will over-run your cartridge. JMHO.