We're planning on adapting our combat rounds to something similar to 4th Ed., where move actions are exchangable for swift actions and standard actions are exchangable for either move or swift... ultimate resulting in the following options for a combat round:
1 full round action
1 full attack action, 1 swift action
1 standard action, 1 move action, 1 swift action
1 standard action, 1 swift action, 1 swift action
1 move action, 1 move action, 1 swift action
1 move action, 1 swift action, 1 swift action
1 swift action, 1 swift action, 1 swift action
To accomodate this change, one of the main things we've done is rule that Quicken Spell allows you to cast a full round action spell as a standard action and a standard action spell as a move action.
What other significant pitfalls can you imagine might come up?
The biggest Pitfall from my perspective would be: Several of the Groups I GM for would be cross eyed keeping up with 'What Actions Do I Have Now' syndrome.
If your players and you can keep the book keeping aspect of it moving smoothly during the game, I see nothing wrong with it. Kind of a cool idea.
Good luck with it and let us know how it goes.
Have Fun Out There!!
~ W ~