My shop, and a few shops around it, has adopted an "Augmented Commander Rule".
The purpose of the rule is to expand the available commanders for players to use, so that you might better be able to find and play with just the right commander. Below I will post the Augmented Commander Rule in its entirety for others to use in their playgroups, and maybe spread it around to others!
...~*'The Augmented Commander Rule'*~...
Any permanent or group of permanents that can, at any time, become or produce a legendary creature may be permitted as a commander. These permanents are to begin in the Command Zone in their original state. When these permanents are returned to the Command Zone for any reason, they are returned in their original state as well.
Permanent groups, such as the Kaldra Items, must all begin in their original state in the Command Zone and be returned to the Command Zone in their respective original states. These groups of permanents may be cast from the Command Zone individually, or as a whole. The mana tax for returning to the Command Zone will only apply to one of the permanents in the group, to be chosen at the start of the game.
If a permanent that produces a legendary creature (which serves as the commander) is removed from the battlefield, but the legendary creature is not, it will not be able to return to the Command Zone until the legendary creature (i.e., commander) is removed from the battlefield as well.
The permanent or group of permanents that become or produce the legendary creature (that is to be used as a commander) are used to determine said general's color identity. If the permanent or group of permanents is colorless, but becomes or produces a colored commander, the color identity of that legendary creature will determine the color identity of the deck.
Any planeswalker card may be used as a Commander. For transforming/two sided planeswalkers, both sides determine their color identity (i.e. Garruk Relentless is a Black/Green commander). When a planeswalker being used as a commander reaches zero or less loyalty, they may be returned to the Command Zone as a replacement effect the same as any regular commander. Nissa, Steward of Elements (and any future planeswalker with X in their cost) has the commander tax added independently of her X cost. For example, casting Nissa, Steward of Elements for a second time would cost 2UG(X).
The following five planeswalker cards have been determined to be too powerful and/or take away too much of the fun/casual aspect of EDH to be used as commanders, and have been banned from use.
---Liliana of the Veil
---Jace the Mindsculpter
---Tezzeret the Seeker
---Karn Liberated
---Narset Transcendant
Additionally, any of the five Nephilim may be permitted as a general, but shall be treated as though legendary (The 'Legend Rule' will destroy them).
Phage The Untouchable may be cast from the Command Zone as though from your hand (you will not lose the game for casting her).
Haakon, Stromgald Scourge may be cast from the Command Zone as though from your graveyard.