Palm has traditionally not provided upgrades for the OS either for free or otherwise. And since now, Palm Source is the developer of the software versus the hadware - I doubt that Cobalt will be available for upgrade to the T3.
There are some interesting comments
here at the Palm Source site that discusses the differences.
I would think that an upgrade to 5.4 would be a "maybe" instead of to Cobalt.
But this is one of those threads that's going to generate several opinions and wishes.
It would be nice for Palm Source to provide upgrades but there isn't any prior historical proof that they will.
They did do some minor updates in the past but these were from 3.0 to 3.5 upgrades. I've never seen them opt for others.
EDIT: Their will be a new HotSync Exchange feature that will include "drag and drop" install for JPEG and Word files according to the blurp.....so perhaps a device is just around the corner since Dataviz just updated to version 7.
Cobalt also includes USB support that appears to be different then Garnet's so I'm wondering if we won't see a new hardware platform that's not been conceived yet.