I find more useful the FF option, with 2x 4x 8x 16x 100x ... I have get used to MP jump system, but the "normal" FF is more useful if you are looking for a certain moment...
Writing our own directshow audio renderer. A huge task as there is wide range of audio devices available, no documentation from MS how to do it, and lot of different audio formats (like spdif pass thru etc.) that should be supported
Figure how MS DVD Navigator manages to trick the directshow audio renderer to allow >2x playback rates
2nd one is feasible but not me or anyone of the devs have figured out how it could be done.