- Give Assault Marines a few AoE knockdown special attacks that trigger often, perhaps a circular swing of a chainsword or jumping on the spot.
- Reduce Assault Marine cost to 500/0.
Hopefully, this would make Assault Marines a capable anti-melee unit that fights by getting stuck in rather than delaying melee. Rather than fighting other melee units by matching their health and damage, they repeatedly knock them down to minimise incoming attacks. This fits in with the disruption role of Assault Marines while still allowing them to go toe to toe with other melee units for a reasonable price.
Against Slugga Boyz, Banshees, etc., Assault Marines would knock them down and wear them down while only occasionally taking any hits. Against ranged units, however, they would lose, even with their initial jump. Why? Because of their cost. If you have two ranged squads, the ASM hit one and render it useless while attacking them. However, their relatively low DPS means that the other ranged squad will gun them down while they attack the first one. If you blob together your troops the Assault Marines can disrupt multiple squads at once and render your whole ranged army useless, but who really wants attack move Tactical blobs to be uncounterable?
Assault Marines costing the same as Tacticals would make them a much more inviting option and let you get a squad straight off the bat, adding some unpredictability in games involving Marines. Being able to make an ASM squad straight off the bat lets you combat early melee, which means that your enemies have a reason to make ranged troops.
Of course, this is all theoryhammer, and may not actually work out, but I had the idea and thought I should throw it out there.