I would love to see the H.U.2 mod weapons added to the game just for variety even adding the ships for the covenant would be amazing, atleast until the asguard and traviler ships are complete by the invasion team.
I would love is events for the diffrent races:
Taur'i to gain acesses to asguard computer core and the Ancient database from Destiny, discovery of the star gate, building the SGC, ability of the Tau'i to Reverse Engineer Asguard, Ancient and Goua'uld Tech. Finding the city of the Ancients. Honestly I could go on and on with the Taur'i. Missions for the SGC.
Asguard discovering the Ancients, the creation of the council of races, the diversion of DNA. War with the replicators, meeting the Taur'i.
Ancients discovering earth, creating the stargate system, builsing of Tao Nas, creation of the council of races, the splint between the Ori and Ancients.
I'm not sure you could do much for the Nox and Ori.
Goua'uld you could do their creation, the discovery of the stargate. Allot of history for them.