It's doubtful that PalmOne will release Cobalt for the T3 because of the seperation between the two companies.
Also, there won't be a financial benefit to do so unless PalmOne decides to charge for an upgrade and that's also unlikely given historical data.
Palmsource could decide to make an upgrade available for a cost but there won't be much benefit for most T3 users to spend the money....unless it's $5.
Plan on getting new hardware bundled with a phone, if you want Cobalt since that's what it really is designed for.