I thought something cool would be if the engineer had just a shotgun, and could fire it, or swing it. Some of the improvements he could receive would be to beef up his shotgun a little. Starting out it does fairly low damage outside of close range because of the large spread, but on hit the target will stagger. The melee is weak but gives you a little distance after a hit.
Upgrades could be cool stuff like...
Undermounted mechanical drill on the shotgun's barrel. It gives good melee range and single-target damage, but slow attack speed makes him vulnerable (I'm thinking he's "stuck" boring into a target for a couple seconds, but it's a guaranteed kill on low and medium armor targets). So you could shoot a group of enemies and get away with drilling one.
Pressurized shotgun shells. Your shotgun deals more damage up-close and adds longer stagger on hit, but has fewer pellets per shot.
