We’ve tried one thing and we are all out of ideas. Better give up /s
Literally none of the things you’ve mentioned are actual obstacles for implementing dual wielding. I have no idea why people are so narrow minded when it comes to implementing dual wielding in particular. The original Bungie implementation failed, so lets do something different, the balancing isn’t especially difficult, its the design of the mechanic itself that was the problem.
How I would approach each of these.
Duel Wielding
Introduce a few akimbo weapon entities that function as duel wielded weapons. The duel weapons act as one entity when dropping and switching weapons. Similar to Counter Strikes dulie elites (pistols).
Elites
Available in all non-ranked playlists. Offer an Invasian/Warzone style Spartans vs Elites playlist as well. Rotate in a ranked 4v4 Elites only playlist occasionally.
Assassinations
Right now assassinations as we know them are entirely a risk-only action. It is only risky because it adds time the attacker is very vulnerable with no reward for successful completion of the action.
Turn them into a risk-reward action. If you successfully assassinate someone then you are rewarded by adding 5 seconds to their next respawn timer. You risk a vulnerable kill animation and you are rewarded with extra time to move around the map.
No need to balance it. Halo is a party game, not a competitive game.
A simple warning when choosing to play as an Elite would suffice - “You’ll be easier to hit because you will have a larger profile than Spartans.” Doesn’t need to be balanced, skilled players will still dominate with it regardless.
Assassinations you don’t have to use you can just smack them if you want the fast kill, assassinations are for the humiliation.
Barely anyone uses small arms anyways, everyone and their grandma has a power weapon in this game, so I don’t see why this would need to be balanced over everything else that is already imbalanced.