1. REs already have Tank Traps which provide green cover so I think the sandbags become kinda obsolete. A combat package upgrade that gives them a satchel sounds practical tho.
2. The Pathfinders already have uhm, "sniping" capabilities so to speak so I think a dedicated sniper squad armed with the M1C Garand sniper is also out of the question sadly and they won't add the Springfield Sniper from the first game.
3. The most they can do is tweak the E8s, again no new models, a lot of people wanted jumbos, including me, but they can only tweak the current Sherman models to the limits of the modding tools which are not much. For example I asked somebody if it's possible to put sandbags on the Sherman and as far as I remember they said that it's not doable.
4. Agreed, Priest really outshines the Calliope hands down. Together with the reason you pointed above with the mortar HT being a reliable anti-garrison unit is why Infantry Company is wayyy more picked rather than Tac Support but I believe they'll need to do a complete revamp in order to fix it while Rifle Company also I believe is due for a revamp as well since it too needs it.
Pathfinders only work in conjunction with arty to deal with mgs. It takes two unit to do the same job as a mortar ht. At that point you might as well go soviets or brits.
I also have issues with tank traps being useless vs suppression. That is why i keep asking for sandbags on rear echelon.