Here's an idea I've been kicking around while reading this thread:
Has a few steps though..
Go with the 3ft square idea, convert all movement to that scale.
Take Iron Heroes' idea of 1/4 of your movement counts for no AoOs instead of the 5ft step. (though the 5ft step needs adjustment as well)
Now you have a 6ft shift, instead of 5ft step. (more movement = more tactical movement, and less static 5ft step full attack.)
For threatening areas, you have around your 3ft square, (assuming a medium creature) a ring of close range, and also threaten the next ring out, long range.
Divide weapons into close range melee, long range melee, and reach weapons. (also some with multiple ranges)
Have a -2 to -4 to hit using a weapon on a target not in its range, like great sword on a guy 3ft from you, or dagger on a guy 6ft away. I didn't crunch numbers, but it sounds fun.
So, a normal medium sized humanoid has a 30ft move, or 10 3ft squares, can move up to 2 squares without provoking an AoO, the same at this speed as the 6ft (2 square) shift and still do a full attack.
Add in IH's skill challenges, and you can do like a tumble or jump check, or whatever is appropriate to the situation, to gain more movement for one round, then a 40ft move gets you 3 squares to move without an AoO, 50ft move a 4 square move, etc.
Then you have 6ft corridors, where 2 guys stand and fight side by side, and it looks real enough, plus you have wiggle room for having more action than 5ft step, full attack, 5ft step, cast spell, etc.
You can still have 2 opponents holding each other at arm's reach, since both are using great axes, and one guy can ditch the axe, quick draw a short sword and get up in his face with a 6ft (2square) shift.
Reach weapons will kind of be threatening more area, but opponents have a bit more movement to get by, if they can.
Might want to go with Tumble as an opposed roll as well.
You might need more room on the table for the battle mat though. I'd give up my dice, paper, and snack spot for something like this.
