Scrounging supplies wouldn't be a good use of screen-time. Feints, probes, fighting withdrawals, parleys, truces, surrenders and ransoms, on the other hand, seem much better plot-wise than watching half the combatants destroyed irreparably every 80 seconds.
Focusing on a single planetary campaign, or some subset of a planetary campaign, also sounds good. Even better (like Knightmare was saying) if it's in an era (like the 3rdSW or Dark Age) where House Lords take a back seat to the local strongmen... which also negates the need for pointless or confusing faction-specific details.
Or set factions to maximum and set it in the Capellan Crusades!
And have a Clan Warrior along. Not in the best 'Mech, and never make any effort to explain Clan culture. Just along to be the weird alien who acts & talks & expects different things than the other protagonists do.
PS, another fan video (the german one with the woman on foot):
http://www.youtube.com/watch?v=Al_SlO5DAkwTo be perfectly honest, I'd put even money that a writer would find the Dark Age an even easier starting point than the morass of tied up and bundled history that is the Third Succession War. We're talking about a war spanning decades, versus a period of time that can largely be summed up as "Apocalyptic war. Enforced peace from new faction. Humans are idiots. Here we go again."
Okay, to be fair, more than a few eras can be summed up that way. But the 3rd SW has a whole lot of relevant back story and side stories tied into as near integral. I don't see that same issue with the Dark Age.
Which back and side stories are you seeing as integral? I can see how Anton's Rebellion would affect everything in that region for a while, but otherwise most campaigns seem pretty compartmentalizable. I mean, it's not like the raid on Galtor is really going to have a noticeable effect on a movie or story set +/- a few years somewhere else on the Kuritan/Davion border.
I dont see DaTR having a unseen issue. Just use the reseen.
That assumes (like someone pointed out up thread) that the movie won't redesign the models anyways. Best notion might be to design completely new 'Mechs for the movie and preview them in a BT publication shortly before release.