What about supporting .ogv files also on megaflashromscc?
Decoding OGV on MSX is naturally possible (although not easy), but the time it takes is a bit of a problem... I would estimate that decoding one minute of OGV data would take something like 10 hours (= ~ 0,0005FPS)... I think that would ruin the play-ability a bit too much.
This could be naturally boosted with dedicated hardware... ie. in PC world they used PCI MPEG decode/encode cards in Pentiums before PC's got enough power to decode the video with CPU or GPU... OGV is better compressed format compared to those times MPEG files, but same theory could still be used although I expect that such a dedicated chip would end up costing quite a lot of $$$ and if you would run this trough MSX & V99X8 you would still end up to about 3 FPS that is about 1/10 of the original speed. In real life I would say ericb59's solution is maybe a bit complex setup, but still a best approach. (And it also gives better picture quality)
How about using that dragon's lair intro full-screen screen 2 video "codec" of yours Nyyrikki, for the video files? And use HW sprites for the OSD (obviously the converted video needs to account for OSD colors).
Ofcourse this would be more like remaking the game instead of a simple conversion.