Gapless Audio...
This is not a weakness of the iPod. It's a weakness of the mp3 and AAC formats which do not support gapless playback on any kind of device. You could sort of hack gapless playback for mp3 if you used LAME as an encoder with a special extension that created a fancy table of contents file. Then you needed a player that was capable of understanding the extra file (I know of a plugin for WinAMP, but that's about it). No hardware mp3 player will ever be capable of true gapless audio. It's just not possible the way that mp3s are encoded.
If you want gapless audio, you should use OGG or one of the lossless encoding formats (which don't really support gapless audio so much as they don't get in the way of playing gapless audio, unlike mp3 which makes the task downright frustrating).
I've heard rumors that Apple was toying with AAC to try to make gapless audio possible, but I doubt they'll ever get it just right. AAC's compression suffers from the same shortcomings as mp3.
Bottom line: It's not the iPod that doesn't support gapless playback. It's the music you're playing on it.
An Equalizer...
Electronic EQs suck first off. True audiophiles won't settle for anything that isn't analog. Secondly, EQ circuits draw power. If you want better battery life in your iPod, you want EQ presets. If you want a better EQ, you're getting lower battery life. If you want battery life and a better EQ then you want a bigger iPod with a bigger battery.
A sports iPod...
I hate to break this to you, but a HD is not "able to absorb the shocks of a mountain bike excursion". You really shouldn't even go jogging with your iPod. Hard drives are pretty fragile devices in reality. Lots of shocks and bumps and crashes will tear up a hard disk pretty well. The iPods counter this by only spinning the disc when reading data into the cache, but still, the iPod is not designed for mountain biking (or snowboarding contrary to Burton's jacket).
A true sports iPod would have to be solid state. The hard drive models are just not intended for that kind of rough treatment.
4 Wishes for the gen 5 iPod