* Hybrid Mana Symbols- the group is somewhat split on this, what seems to be the majority feels that it would be okay to allow the inclusion of hybrid mana symbols with part of it being in your commanders color identity (for example- Rubblebelt Raiders would be legal in either a Purphoros deck or a Rishkar deck).
I was always a little torn on that too. There
used to be two different rules that limited Commander decks. First was the rule (that we still have) that says that a card's color identity cannot be outside of the Commander's color identity. Second, there was a rule that said that a Commander deck could not generate a color of mana outside of its Commander's color identity. When that rule was in place, I always felt that the hydbrid mana (among other things) should be allowed. It was impossible to cast
Rubblebelt Raiders with green mana if
Purphoros, God of the Forge was your Commander.
But with the advent of colorless mana as a cost, that other rule was done away with. Now every deck can generate all 5 colors of mana. I am now against allowing off-color hybrid mana.
While it is usually corner cases where you steal an opponent's mana rock or something, it would permit you to cast hybrid spells using mana colors outside the Commander's color identity.
Also there's the issue of other "sometimes off-color" cards ... split cards, aftermath cards, cards with in-color mana costs, but off color activations. I'm sure the list could go on. It isn't a stretch to see that going down that path could allow you to abuse cards that shouldn't be in the deck to begin with. (Although, if that is what you are going for then go for it!)
I also believe that the spirit of the color restriction in the Commander format is to inspire creative deck building choices. The fact that people want these cards in their decks tells me that these are the superior cards for their build. Creative deck building seeks to maximize the inferior options.
Happy Brewing!