On a different subject a long time RFE has been the ability to customize the tabs using a more powerful API. The main blocker for that has been the hardcoding of Buttons (or really radio buttons) as tabs in the Tabs component.
With the upcoming version of Codename One you will be able to replace the usage of Button with just about anything by overriding a set of protected methods in the Tabs component. These effectively allow the Tabs class to understand the structure of your potentially complex class and communicate the requirements of the component. In the relatively simplistic implementation below I just used a layered layout to place a close button in the right side of every tab. This is code I used in the kitchen sink demo to test this effect.