As ought to be obvious from reading the results of various campaigns/wars since WW2 everyone has been poorly structured for the next conflict. The best plan is to take a best shot at preparing for the more probable but keep something in your back pocket for the less probable. There's a very steep learning curve to reestablishing a needed capability once the last officer and NCM who knew how it worked retires.
We can currently do a good mixed light regiment with a couple of G1 batteries and an M777 battery or two. It would be nice to pick up some LINAPS to let the G!s self locate and orient. Could use some 120mm though.
Incidentally, I don't think an HMMWV is an answer for the M777. It can only tow some 4,000 lbs and the M777 "ultra" light howitzer comes in at 9,300. And then there is the ammo. The civvy Hummers do a lot better at between 7,500 - 12,000 lbs depending on version) The LMTV, at towing around 10,000 lbs is okay as long as the terrain doesn't get too rough. I read that the US gave LMTVs to the Ukrainians to uses as gun tractors but I wouldn't want to go below that and you'd need extra vehicles for ammo and anything over a minimal detachment.
I think the US TOE calls for the M1083 MTV rated at around 21,000 pounds which has the guts to tow the gun, carry the crew and a decent load of around 80 to 100 rounds. There are no dedicated gun limber vehicles for extra ammo, just the battery's five M1084 (MHE) ammo trucks and trailers. Canada uses the HLVW as the gun tractor and ammo carrier. We tend to put the crew in a separate armoured vehicle but I'm not so sure there are any around.
@markppcli might know better where things stand now.