I think it would be interesting if all modes (Control, Clash, Rumble, Skirmish, Combined Arms, Salvage, and Doubles Skirmish) were available during Iron Banner. Inferno could also prove an interesting addition.
Make it random, though restricted based on fireteam size.
1 - anything
2 - all but rumble (debatable for 2 and 3, since you can join in normal)
3 - all but rumble and doubles skirmish
4+ - Control, Clash, Combined arms
If nothing else, it would add some much needed variety to Iron Banner. I'm sure the next Iron Banner is coming up too quickly to implement this, but it would be interesting to see in the future.
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Iron Banner Suggestion: bring it back!!' And include a 32 helmet and sparrow. I want them. I also like the variety you listed. A+ suggestion.