Personal opinion, perhaps, but it would seem to me that the various Mechwarriors (some with neurohelmets) would be a hot seller for RPGs, either for player characters or NPCs trying to get to their 'Mechs, or for ejected pilots trying to evade death or capture at the hands of enemy infantry on an active battlefield. The other factions' ground troops (besides Davion and Kurita, who already have infantry sets) might be second most useful, and the various techs, security guards, etc., third.
Of course, different players will have different ideas for games they'd like to run, so I could be totally wrong. It might be interesting to see which of those figures would draw the most interest.
To weigh in on a couple of earlier comments, the sculpts are reasonably good enough to still fit into a relatively modern game, but not at the high end in quality. Basically, they're more than adequate for almost all purposes besides painting competitions, and I don't think we could expect to see IWM pay to have anything better sculpted in any reasonable timeframe, if ever. I'll take "good", if I can't have "great", because it beats having "nothing".