They were ridiculously overpowered for squad combat considering they were supposed to be for taking out facilities. Presumably once facility combat comes in they will be tweaked to work with that better.
I know this is still a long way out, but is there any idea of the skill set that will be required to successfully deploy a bomb? I know there used to be a formula for damage based on repair skills and deployment was based on computer ops (if I am remembering correctly). Considering the economic system that controls most aspects of the Combine, I think a saboteur would be an interesting character idea, but potential saboteurs have no idea what to work towards.
There have been a lot of ideas and some actually involved no skills at all, just an extra bonus action, but we've got a different dev group currently and it hadn't received any discussion at all due to other priorities.
It hasn't been developed at all so that's not a question that can be answered. The likelihood of it using the grenadier NPC is equal to the likelihood of the grenadier NPC type being removed when useless NPC types get purged. Personally I suspect the latter but it has not been discussed.