What I would like to see for the N900:

1. improved battery life (6 to 8 hours of online activity over WiFi/BT or media playback over BT A2DP)

2. improved performance -- if going from 320Mhz to 400Mhz gives this kind of improvement, I'd look forward to going up to 520Mhz

3. native support for A2DP (yes, I know this can be sort of done today, but it requires a couple of arcane commandlines and it still has limitations)

4. support for two SDHC cards, or maybe even 1 x CF and 1 x SDHC. CF prices are plunging on a per-MB basis, and if Nokia starts adding PMP to the positioning statement (thus making it Media Meets Internet), the N900 would fly off the shelves