Ratskinner
Adventurer
I'm not concerned about the speed of play... I'm more concerned about what each player can do on his turn.
Yes, speeding actual gameplay up will help ameliorate some of the problems (by having turns come up really, really quickly so there's less downtime)... but that doesn't change the fact that WHAT a player gets to do when his turn comes up is going to be 50% movement and 50% attacking for mobile PCs, and 100% attacking and 0% moving for frontline ones. And since the attacking is traditionally the "fun" part of the turn... mobile PCs are only having fun 50% of the time (even if that time moves pretty quickly).
When you have both a Standard action and a Move action in your turn... a mobile character gets to do both each and every turn. They still get to have the "fun" part every time their turn comes up. Sure, the frontline character ends up "wasting" a Move action each turn because he never moves... but because moving isn't fun anyway, it doesn't MATTER to the player that he's "wasting" it. He's still getting to attack every round and the "lost Move action" is an afterthought.
That's my only concern by merging the Standard and Move into one single action per turn. The mobile PC potentially loses half his attacks compared to the frontliner.
Don't you think that if a player chooses to play Mr. Mobile, that he must think that moving around is fun, too? I mean, your concern is based on the theory that attacking is fun and moving/position is not. Certainly that's something that varies from person to person, and up to them upon character creation. My guess is that Mr. Mobile's player would be perfectly happy with fewer attacks, especially if those attacks had bonuses attached to reward all that moving around and positioning.