One POSSIBILITY I'm thinking of is using the same system but reversed in order for shooting, with an additional caveat: any damage done takes effect AFTER all units of that type have fired.
For example, you've got an Awesome and a Locust. They have two Javelins. The shooting goes Javelin, Locust, Javelin - and all damage takes effect, so if they critted the Awesome and removed a PPC, it wouldn't be able to fire that PPC once its own turn rolled around.
I dunno. I'm still ponderating this, especially the second part - giving lights the movement advantage would probably be more than enough. It would be a HUGE shakeup in the rules.
I don't like this second aspect at all. It feels like taking the mistake some people make about resolving declared fire right away, having the target declare and resolve their own fire with all the damage already applied, and compounding it. The Fire Phase of the game is simply too abstract for things like that, in my opinion. If you want to go for things like that I feel that you'd need to make everything far more detailed to keep things fair.
Using that as is, a pack of Lights could be perfectly capable of stomping a heavier 'Mech into the ground without it being able to do anything at all about it, all simply because they are classed as Lights. (And basing that on weight class alone then brings in the silliness of 'Mechs like the Panther and the Hollander having this fire first perk, even against say a Medium that moves at 8/12 or 9/14.)
So you're talking about a "holding initiative" style thing for the infantry, much like in Shadowrun? Hmmm, interesting... the only problem is that allowing held initiative for everything would essentially destroy the system.
If everyone held their initiate then nobody moves. Also simply limit a unit to being able to hold initiative for one tier higher up. If they haven't moved by then, then they are treated as not having moved.
Or perhaps an alternative, make it cost MP to hold initiative. Say 2 or 3 MP? You also have to declare your movement options (walk, run, jump, MASC) the first time you hold initiative.
What about making infantry move last, even after light 'Mechs?
I like this. Much the same reason why infantry don't have a facing to begin with, the one thing that really is in their favor is the ability to quickly come to a full stop and go in a different direction. When added to their limited MP they still can't really use that to threaten a unit that is paying even a modicum of attention to them.
I'd add an option for a heavier unit to move through a hex occupied by just infantry though. Something akin to a charge, where they just try to power through the hex. Infantry being able to pick the choice of either scattering or holding and performing a weapon attack on the unit doing the charging at range 0.
If I've again forgotten some existing rules for that, just use those of course.
But hey, if Worktroll likes it, it just needs tweaking to be fairer. The idea of movement bands controlling initiative rather than weight is a bit complicated, but not bad... something like,
1) 1-5 max MP move
2) 6-8 max MP move
3) 9-12 max MP move
4) 13-15 max MP move
5) 16+ max MP move
Better than just using weight class. Needs more definition though, like where you're taking the MP from. After all, max MP for a turn is only known after a unit declares if it's walking, running, using MASC, and so on, which only happens when they actually get to their turn.
Use something like, base walking MP (after heat effects from the previous turn are taken into account), make the table in increments of 2 or 3, and have extra movement mods (JJ, MASC, active TSM) add a +1 to the rating for the table, perhaps?