...because its home base is going to be mobile somewhere in the WestPac instead of Hawaii or Alaska...
Don't forget Guam and Diego Garcia. Not to mention, they are currently making a deal with the Philippines to establish 4 bases in there, so that's also another set of possible international airbases for the USAF to operate on. Whether those bases will station the NGAD or not, remains to be seen.
There’s a wealth of air bases in the WestPac, but the USAF in my estimation is trying to extend NGAD range (and therefore basing) beyond the second island chain. This isn’t something they have stated, but it does seem to be the direction they are moving in given the range of the B-21 and the way they are training B1 units: keep the most important aircraft completely outside effective PLA missile range. I don’t think NGADs manned component will have the same unrefueled radius, but I think USAF is going to attempt to base them outside the WestPac (I think Australia will be a major location in that regard).
I wonder how it will work out.
Such ranges not only stretch basic fighter missions on the brink of feasibility (case point: IJN fighters operating over Guadalcanal/Darwin - length mission-wise, but also - difficulty of effective SAR for such missions). Also, basing fighters behind key US allies may be tricky. ROC has no voice, but Philippines, certainly - Korea/Japan, possibly - Singapore (who knows where it'll turn) - certainly do.
All of those places would be too close anyway. The idea is to be clear of DF-26 range, or more broadly anything sub ICBM. I doubt NGAD can completely achieve that kind of radius unrefueled, but from a place like Australia, tankers can top off in friendly airspace coming and going. Wake island is another location at roughly the same distance but obviously with a lot less capacity and more vulnerability. The tankers might also simply fly a couple thousand miles before offloading fuel - not great, but taking off from US states still removes the two island chains as a basing liability.
The B-1s are training for round trip strikes to the Pacific - missions as long as ~40 hours. The B-52s can already arguably do the round trip to the SCS well enough from Hawaii or Alaska to get into cruise missile range (and their range increases by 25-30% with new engines). And the B-21 is explicitly being sold as a platform that needs no basing or logistics in the WestPac, which giving the emphasis on range requirements for the NGB and LRS programs (along with the twin engine selection, modern structure and engine efficiencies, and likely downgrade of payload for additional fuel) make me think that it has an unrefueled radius that reaches out to HI/AK.
I think NGAD will follow in this trend of making the most important USAF aircraft based in the US itself either by extreme range or being supported by tankers in theater and accepting the risk to tankers (more disposable/less expensive) such that all of the most expensive/important aircraft never actually live in the Pacific theater. Or if they do, it is to land and hot pit refuel/reload with pre loaded rotary launchers and be out in a couple hours or less. I think NGAD will have a range around 2000mi/3000km. In even an F-111 sized airframe, that wouldn't really be that challenging if you didn't worry about maneuverability - the F111 got about half way there while managing to be supersonic capable half a century ago. With a more efficient shape, composites, and adaptive engines I don't think it is at all problematic to have a 2000mi/3000km combat radius in that weight class. Tank off wake or Australia, or off surviving KC-46s painted white operating from Japan's regional airports, and never ever be on a tarmac within IRBM range. Or do so only for a fast refuel/rearm, for a couple cycles only.
The USN is more size and weight limited and its airfields get to move around, so for them I think the threshold is "outside DF-21 range" and the objective is "outside DF-26 range". But they don't have to find a convenient land mass and then size their aircraft around that requirement like the USAF does - they can always chose their operating range from the enemy coast. So while they want to push their range out, they can always tailor the range of their airbases to meet the threat. And especially given the UAV tankers, they are likely not going to have combat radius requirements as extreme as the USAF (just my personal guess). And their space, weight, and stall requirements, as well as the structural requirements for aircraft recovery, make their aircraft a completely different beast than the USAF as well. Hence my belief in two separate programs and airframes for the manned component.
On top of that the USN is going to have a very different environment for UAVs - it seems likely to me the USAF might adopt something rocket launched/parachute recovered in theater, with perhaps a B-52 air launch option, rather than build a UAV with a range to match the manned NGAD component. The USN on the other hand almost certainly wants to colocate those two items and launch and recover them the same way, with all of the drastic differences that come with that.
That said, the avionics, basic airframe structures, coatings, and possibly to some degree engine tech easily could have a lot of cross platform utility. For engines, probably different models/manufacturers would be needed for different platform sizes, envelopes, and range considerations. But if you make a smart skin elements for ESM or a T/R AESA modules and just put more or less in a given radar for the size of the airframe, you can scale a lot of the avionics to the size of your platform. I suspect B-21 uses the same T/Rs as APG-85, just because Northrup makes both and why wouldn't you? Except in the B-21 they are probably arranged in a much larger pattern in cheek and tail mounts rather then a single nose array. But once you are cranking out T/Rs, why not use the same building blocks for other arrays as the SPY-6? Add more processing power as needed and build a different capability to suit the airframe and mission.