It's obviously not inevitable for armies to widely deploy mobile C-UAS systems, but why does it have to be in the form of a SPAAG?
A SPAAG dedicates most of its usable space and/or mass, as well as crew attention to its complex firing system, which unfortunately is comprised of just one element.
In the modern battlefield there will be an abundance of medium caliber cannons, machine guns, and other shooty stuff. So why do you need another medium caliber cannon but this time with a crew that doesn't know any other mission?
A proper modern SPAA should strive to bring NEW tools, such that other AFVs don't have, like powerful sensors and jammers, long range drone interceptors, microwaves and lasers and all sorts of stuff industry's pumping out to fry drones.
There are M-SHORAD Strykers and JLTV assets, we have the future multi-mission launcher/USMC Iron Dome variant, and Patriot of course, but those are all short and medium to long range static positions requiring separate launchers, trucks, radars, and control centers.
We have C-UAS drones in all forms, from offensive explosives, energy weapons on drones, net launchers, electronic warfare and so on. Then there's various programs like reusable jet engines powered missiles that can land if they didn't intercept, dedicated microwave weapons setup for both static defense and mobile variants (Stryker again I believe). I believe the US Army and USMC both have JLTVs with basic auto cannons and energy weapons/electronic warfare variants being developed or manufactured now. I'm sure they have both offensive and defensive cheap drone swarm programs in development. However, with all that said, given the performance of the SPAAG in Ukraine, and then the existence of these units in EU, RU, and Chinese militaries, I think there's a use case for them in the US inventory, particularly when I believe the US can make them much more effective over the units seeing success in Ukraine.
Here's one specific example. We have the USMC moving to Force Design 2030 and Littoral Regiments while requesting the Medium Landing Ship to setup on some of the thousands of small islands in the Pacific and provide defensive areas (apparently) by deploying unmanned systems, the JLTV NMESIS Naval Strike Missile launcher, and then containerized Tomahawk/SM-6 launchers etc. I believe a SPAAG (as described below) would be a great option to deploy with such small isolated groups for inherent anti-air defense (incoming aircraft and cruise missiles for example).
I believe a modern dedicated SPAAG with st least two medium calibre (at least 35mm, preferably 50mm) auto cannons with the new dual-feed capability, allowing selection between proximity fused AA munition and high-explosive/fragmentation/anti-armor all purpose rounds would be a great assets. Both would be programmable rounds coming out of the barrels to enable both more effective AA rounds and also allow for those all purpose rounds to explode above or behind infantry cover (or even trenches if NATO/US forces to go against trench defenses someday). I believe that type of capability would be welcomed and be useful to fill in any gaps in our current mobile M-SHORAD solutions. Particularly as there aren't a ton of those Strykers and JLTVs out there, per my knowledge.
The capability to fire on the move at any air target and also destroying nearly any target on the ground with intimidating firepower, if called upon (just as the VADS rotary cannons were known to be devastating to hit ground targets, as the air threats were nothing like today).
Taking that and combining it with modern US fire control systems and sensors/optics with a stabilized turret. Then adding either supplemental radar-guided Hellfires/JAGM/NLOS or APKWS II guided rockets (a recent Warzone article shows the rockets are accurate and agile enough to take down drones from Yemen being fired from F-16s) would also add missiles/rockets that have dual use on the air or towards ground targets. And there's always energy weapons you can add to enhance a SPAAG.
In particular, the USMC doesn't have the Stryker, their ACV doesn't appear to have anti-air capabilities planned (just a 30mm autocannon variant with no mention of C-UAS), and their potential LAV replacement IFV that does specifically focus on their C-UAS variant in their proposed lineup, may not happen now. If it does survive, production won't be until 2030 (the program is loosing momentum per recent USMC officer comments and articles).
Using the AMPV platform should have the adequate speed, mobility, and core systems to add an unmanned turret and have the necessary auxillary power for those secondary systems/onboard radar/sensors, and so on.
I think opening up the AMPV platform to help out the USMC while building some of those same platforms for the US Army would give the forces some added capability, firepower, inherent anti-air capabilities, and utility while using a proven platform in the AMPV (per full production status), only requiring the turret and added systems integration vs. developing an entirely new platform.
