Basically everyone throws out suggestions they have for new Heavy weapons. I'll go first:
Magma Cannon: Basically a heavy Hades. A long range, multipurpose weapon. Maybe some side boilers, a magazine loaded from the back of the gun would be really cool. Slow fire rate, applies 5 fire stacks (maybe less?) On hit, bursts of steam when fired and reloaded. Rounds would look like Hades rounds, but longer, bigger, and they'd leave a trail of fire/black smoke.
Jupiter Field Cannon: Basically a heavy Mercury. Would take a long range piercing weapon role, with a clip of one, average reload times, and a little projectile drop. REALLY loud boom when firing, arm sized shell casing ejected when reloading.
Vulcan Heavy Repeating Cannon: Mix a Heavy Flak and a Gatling and you get this. Dual rotary cannon, Shatter main damage. Clip of 50-60, medium spread, maybe a little under the light gat. DAKKA noise when firing, long reload time, heavy screen shake while firing.
Net launcher: Four holes with metal balls with balloons loaded in them, and in the cracks between, lays a net. When fired, it would have a mine like arc, and a huge spread. The balls, after reaching a set distance, would expand the balloons and tense the net. Someone flies into it, they are dealt flamethrower speed damage to balloons and engines.