Thats all good but at this time we are not getting SPH and there is currently no plan to get SPH. The problem with SPH is they are Tracked Vehicles unless you go to the Gun on a Truck which still req the Crew to get out of the Truck and set up the Gun before firing. While Tracked SPH are great on the Battlefield itself it still req Low loader Trucks to get them there and like all Tracked Vehicles they req a lot more maintenance than Trucks do. They can't shoot 300ks so useless to you if you don't have enough Low Loaders to carry them.
Towed Arty are not obsolete because they are much easier to deploy over any real distance, how do you avoid Counter Battery Fire, take theirs out first by providing better ISR & Comms, get the first shot in. That is what the ADF is working towards, history has consistanly shown the side that shoots first wins most battles.
We will have to wait for the next DWP to see if we get some form of SP Arty, A 120mm mortar on some of the Land 400 IFVs maybe to supplement the M777 but not replace them
The only ADF Aircraft you can put a SPG on is the C-17, you can put M-777s on C-130s and C-27s.
The great strength of Towed Arty v SP Arty is deployablity. The great weaknes of all Tracked Vehicles is that deploying them away from home is a bitch.
I don't disagree that Armoured Units should have SP Arty, just your suggestion that Towed Arty is Obsolete.
Addressing in order:
I don't really care what Army has now as anything more than a means of identifying what, in accordance with Government direction and the assessed future operating environment, Army needs. SPHs don't feature in DWP 16 sure, but that doesn't mean that there isn't people building the body of evidence needed.
SPH does not mean tracked. Right now there is a Boxer 155 mm module. The South Africans have the G6. If that meets requirements, good - buy them. If a K9 or M109A7 or AS90 does better,, than fine, buy that. I don't care what it looks like.
For me, SPH is not a gun on a truck. One of the advantages of the SPH is the protection for the crew. Buying a gun on a truck is a stupid way of filling the gap.
Maintenance is not a function of wheels v tracks, but rather weight. Up until now, tracked vehicles have traditionally been heavier than wheeled. I doubt you are going to see discernable differences between IFV and CRV. Furthermore, I am already lifting tanks, under armour breeching and IFVs. I have something like 800 heavy tractors in service now; I'll buy another six trailers at $50k to move the SPH. In a program that will be 8 - 9 figures, who cares about another $300 - 500k?
Deployment is a function of what mode you use. A Boxer or G6 can self-deploy easier than a towed gun. I've already bought 6 trailers (that are easier to move around than a gun), so that's not an issue for tracked. By air is a problem for our whole force, do we honestly think we will C-17 in a Bde? Even a mech BG? And sea? Just drive the SPH on or off - again, easy.
Great, rely on our ISR. In a congested and contested environment with almost every neighbour having weapons that over match the range of a M777, how much are you going to place faith in that. Furthermore, assuming the enemy have similar capabilities to us, just how easy is it to hide our guns? Noting too, that if you want them to be used you have to fire - and you better hope that every MLRS within 30 km has been cleared out. Do you think that's feasible without using the guns?
We need to be clear that a 120mm SPM does not replace a 155 mm gun. They are complementary, not a replacement. If you forced me to pick a 120 mm SPM or a 155 mm SPH I'd go the latter every time. Buying 120 mm and saying that is our SPH capability would be stupid. The mech BG needs a 120 mm mortar system more than an 81 mm; but less than a 155 mm.
I also think it's time to start having a realistic assessment of what the RAAF can deliver for Army. Sure, an SPH cannot fit on a C-130 or C-27, but neither can an M1 hull, a CRV or a IFV. So - who cares? Furthermore, a M777 requires 2x C-130; because the gun tractor has to come too. So now a Battery requires 8x C-130 lifts. Are we going to have those airframes spare? I'm not sure about a C-27 - I think it's irrelevant from an Army logistic point of view anyhow. Can a M777 really fit in one? A MacK?
Towed artillery is at best no harder to deploy than SPH. So getting to the battlefield is a reasonably simple solution for both. But once the rounds start flying, the towed guns die within minutes. SPH can survive. So tell me - what do you want to fight in? This is a F-86 v F-35 question. I'll take the SPH thanks.