It was also my first question that came to mind after the unveiling of the new 3310. I was hoping for a nostalgic throwback to mobile java apps.
However, it seems like the OS (s30+) doesn't support J2ME, so definitely no third-party java apps. I guess there might be a slim chance they'd add some kind of app store by the time they release the new 3310, in which case you could develop apps in MRE SDK (maui runtime environment). If I'm not mistaken MRE is in C.