Slam might detonate biotics in the air (I can't recall from single player), but that's not the kind of detonations it would set off most often.
When I'd bring Javic with me on my soldier, I'd incendiary ammo them up, then hit them with slam. The resulting fire explosions were very nice, since it generally killed them. Those would always occur at ground level, from the impact damage (which killed the enemy, thus triggering the explosion). Not sure if the new mechanic would ruin this or not, but it works well enough in single player. Could use a shield pierce or a stagger.
As far as them not wanting to put work into it, I doubt that. Lash doesn't exist in single player, but there it is in multiplayer. I would be willing to believe a height/tech issue, but then again, you can use slam in single player, and all the base multiplayer maps are present there.
Inevitably, its up to Bioware. If they can, they will, if they can't, they'll simply admit it. Bryan's been pretty good about that, even though I don't think this is his cuppa tea.