I think the lowest hanging fruit is:
1. Writing an OS 9 EHCI driver.
2. USB TracPad support for some iBook's/PowerBooks.
3. A wifi driver for 802.11/G
4. Sound support some Mac's
5. PMU support for some Mac's
I 100% agree with that, although in my opinion we, as a community, should really focus on finishing the ongoing projects, like f. ex. the 17" 1GHz G4 Powerbook.
I mean it's really not that far away from becoming the holy grail of portable OS 9 machines.
If we could somehow focus on resolving its power management issues (like lack of a sleep function and getting a little bit toasty) and resolving the sound issue (so you don't have to plug something into the headphone jack to get the sound from the internal speakers, I mean it's absurd) we would already have the best OS 9 portable ever.
If we could also make the Cardbus slot operational and make the Ethernet port work at its full speed on top of that, then we would not only have the very best OS 9 portable, but an ultimate one.
If somehow, in the unforeseeable future, a support for the 802.11g Airport card, USB 2.0 and FW800 came out... well, we would have ourselves a truly epic OS 9 portable then...
Although I am not able to provide any help regarding coding itself, I'm able to test everything new basically on the spot, with instant feedback.
On top of that, I was thinking for some time now we, as a community, should go the MorphOS way, by which I mean crowdfund bounties for people supplying some specific updates/drivers/rom etc. This way the incentive is there to not only make OS 9 bootable on unsupported machines, but to make OS 9 fully operational on those.