This is a tough one as all three of these systems I had versions of on my drawing board.
With the Daybreaker cannon, MURDER RPG, and the new ATGM, we really can't face their mechanized forces symmetrically anymore. CAS and IDF called in by Scout Snipers is really the way forward strategically. (Literally what the Russians have been doing in Ukraine for the past few years BTW.)
We've needed a good aerial AT munition for a long time now. With with our Firecracker submunitions as a tech base, and the old but reliable Haast as a platform, a duel purpose cluster munition would be the obvious solution. Air deployed minefields would also be a great capability to have. Unfortunately the VVF Q was a complete disaster and we're one good Cannalan design away from losing the skies again.
If we're going the IDF route, MRLS is the way to go. The Sarukh is relatively ancient (1940!) and could benefit from newer rocketry advances (Piracy Warning) and all-terrain amphibious chassis (Salamander) for the Artemis. Jesus, more than triple the warhead and five times the battery size!?! That's an ambitious amount of firepower there, but exactly what we need to commit to IDF.
But what good are IDF and CAS without forward observers? Snipers love being marketed as killers, but are also invaluable recon assets. Worried about RPG and AGTM ambushes prior to a mechanized advance? Send the Scout Snipers a day before. They'll be dialled in to take out AT teams the day of the advance. Give them a radio and they become amazing FiST'ers. Put them on a stealthy LRS/LRRP mission and they've find all kinds of shit to rain fire upon. .60 cal is overkill, but probably more efficient than developing a newer rifle cartridge. The recoil on .60 cal is probably too ridiculous for semi-auto so might as well go bolt action for reliability. If we get a solid roll on what shouldn't be too difficult a project, we could get optics for our assault rifles too. The last time we fought in mountains, the battle report really stressed how neither side had cheap scoped rifles.
It's a tough call between the MRLS and sniper system + universal optics. I'm going for the Horsekiller and hope our commanders know how to use it correctly. At the very least, we're sure to get a battle report with a guy's head being blown off.
(3) UF-MLRS-43 "Artemis" : QuakeIV, VoidSlayer, Jilladilla
(4) Horsekiller Mk II: eS, Powder Miner, Happerry
(1) Grapejuice Cluster Bomb: Wizgrot
(3) UF-AMR-43 Horsekiller Mk II B: NAV, NUKE9.13, Kashyyk, Conscript Five