Man, this issue drove me nuts when I first read it in the rules! I've been thinking about it since then... but now that i've finally got the registration sorted out lets do this.
A lot of it comes down to trying to figure out what kind of frames take dual movement.
Move-shoot-move would be a really cool mechanic for direct fire units; but not very useful for arty or HtH. I think the suggestion for ramming would be a heck of a lot of fun, but adding a second additive bonus in addition to spot for melee would result in a lot
of totally crazy one-shot kills (and also doesn't do anything for shooty guys.)
I'm going to suggest that The first time a frame with is attacked, it may ignore one damage by moving away from the attacker 1 unit.
I feel that this works for melee and ranged - they both benefit from the defense; though ranged units also probably enjoy the bonus move away from attacking HtH units. It's simple (you already know if this is the first time a frame is attacked because you would have just placed defense dice) and is a variation of an already existing rule (the retreat from stations rule, which I've always felt was out of place.)
I like that it adds a bit of depth - 2D6G frames are brought down by repeated attacks instead of the spot + attack required to damage D6B frames, giving a bit of strategy on that front while also opening up a use for frames that attack without spot support. 2D6G frames with this rule are at an advantage in 1v1 confrontation, making them good at chasing down other frames. It makes 2D6G frames CONSTANTLY moving, which fits the move speed bonus, and even fits fiction really well - it's a dodge, and it reflects that you can't specifically dodge when multiple people are attacking you. (To the people who say that
also represents a dodge; how often do you see a frame modeled with dodge capability counting as a D6B?)
I'm really not sure if it should stack with the station ability - on one hand, 2D6G frames are ideal for capturing stations, so the ability should support that. On the other hand, ignoring two damage is totally nuts
The only downside is that it is bringing another defensive ability to the table, which is a pretty harsh no-no. The only saving grace is that these frames probably won't be stacking defense, and I don't feel that it is too powerful - two systems is a HUGE investment and movement is one of the more situational systems to invest it in.
EDIT: note that while this has the potential to take a frame out of cover, the attack that moved the frame happens frame's move so it's not really an issue. (especially with 2D6G) A bigger issue is the loss of range for H2H units... but two inches is a lot better than a system 90% of the time. (and imagine the tension if you have a HtH frame six units away and it takes a hit.. do you drop a system or require a really lucky D8 roll? Now that's a fun decision)