Sorry to barge in late to this thread.
The Germans in WW2 had a vehicle that basically filled this role: The Sd.Kfz 251/9. This was a fire support variant of their standard infantry-carrying halftrack equipped with a low-velocity 75mm gun (the same one as on their early MkIVs). Each Gepanzerte Panzer Grenadier company had two of these vehicles. For the Germans this was, perhaps, a natural extension of the Infantry Guns found in their Infantry Regiments.
I can see the point in having such a vehicle, but whether it would fit in the Canadian Army is another matter. The 25mm certainly gives integral firepower to the infantry platoon/company and tanks working in a combat team setting provide a tremendous level of fire support. Would the added benefit of a LAV with a Cougar-esque turret outweigh the cost of adding a new vehicle?
I see the main benefit of a dedicated low velocity fire-support weapon during offensive operations to neutralize strong points. If we are conducting offensive operations then perhaps we can dicate the time and place and can thus have a greater chance of being able to call on our tanks to support said offensive operation. Would two or three added systems with low-velocity weapons provide true value-added in a combat team? Would a LAV company go it alone without tanks but with fire-support vehicles?
I think that I would rather see integral anti-tank assets (medium to long range) re-introduced to an infantry battalion before fire support. Having integral anti-tank capabilities means that the tanks can be concentrated instread of spread around to make people feel safer from enemy AFVs.
Having said all that, when I was overseas I saw the potential benefit of MGS as a fire-support vehicle in a tank-less theatre. Seeing as we were able to get tanks into theatre, though, I'd just as soon focus our resources on some other areas to replace aging fleets.
Regarding the distribution of tanks, I see the benefit to having a balanced fleet across the Army - ie having a tank squadron in each CMBG. Specialized brigades can work for one-off operations, but I think that our Army needs to be built with general-purpose as the guiding principle.