My primary reason for this suggestion is to remove static mortars entirely. This is due to the negative impact they so often have on the over all team by way of tying up resources i.e logi trucks, manpower (often a full squad when it's coupled with a superfob), and radio exclusion area.
However, for all you mortar fans, I am also suggesting adding even more mortars to the game.
So firstly, I suggest that infantry mortars be added. Typically a man-portable 50-60mm (M224, M6, RM-38 etc) mortar and give them about 10 rounds (subject to balance, refillable from ammo bags). These can be used in a squad push and can be effectively ordered and directed by that teams own squad leader. This creates stronger team work between SL and mortar man and will lead to faster engagement times and overall more effective mortar support at the squad level.
Secondly, add vehicle mortars (81-120mm). This adds the punch back to mortar support and re fills the map wide/team wide mortar support capacity while also being more flexible in that they can rapidly redeploy when the front pushes out of range or the enemy gets too close.
Also most of the existing vehicle mortars in the real world are variants of vehicles we already have in game i.e BTR (Nona SVK), LAV (LAV-M), Stryker (MC), make shift technicals for the Militia/Insurgents could be made (similar to the rocket arty technical).
Both types of mortar support that are called for in Squad are covered by these two options, that being smoke/barrage just before a push and fire for destruction of emplacements/HAB. All done with greater flexibility and with out tying up valuable resources, and I would argue being more enjoyable and rewarding those playing the mortar roles.