Could one see designers of future scenarios SSR a 80+mm Mortar OBA Module?
I would not consider that unreasonable.
70 vs 80 battalion mortar OBA! What is that in terms of "realism"?
It's really some form of OBA that is dedicated to the unit that is just 1 level above what is usually within an ASL player side. Purely off the top of my head, I'd say up to a half of scenarios have only about a (reinforced) company, the common 6 to 12 squads. So that ASL company is much more likely to get assistance from it's parent battalion than its regimental or divisional OBA assets who are likely to have other customers to serve.
It's the priority that your on board ASL unit has with the OBA that really matters, not whether it's battalion or not. Indeed some armies like the Japanese and Romanians (and even the Soviets during scarce times) might have no medium mortars at battalion level. When the Germans reused and eventually made copies of the Soviet 120mm mortars, they issued them at battalion level and the 81mm battalion mortars were split up and passed on to the rifle companies.
A case could be made that if an army had battalion level mortars or infantry guns that you could give an additional -1 DRM per additional company equivalent on board above one company in addition to the effective -1 for
maintaining contact (1 comp = -2 total DRM, 2 comp = -3, 3 comp = -4). But that's a rule change and too late for that.
However what's not too late is to think less in terms of battalion MTR and more in terms of dedicated OBA, whether it's true battalion MTR or someone has got the undivided attention and devotion of a 150mm howitzer battery. Klas is right, it's what to interpret the firing unit's intentions and orders that really should matter, IE the OBA mission, not the formal OoB tables.
So if Captain Winters slipped the nearest artillery battery commander a bottle of whiskey during his last meeting, why not have 105mm or 155mm "battalion MTR" OBA.