I don't understand why WotC doesn't want to license out any more of their properties, since as I understand it, they are under constant pressure from Hasbro to generate profit, which licensing out IP they have and aren't using would do. Unless they are considering using those properties themselves. If their driving motive is profit, they wouldn't turn away a chance to make money on a property. If they aren't going to even think about selling it, they might have plans for it themselves.
Look at it, WotC might be going back to the Idea Well. Environment books ? Honestly, Frostburn et al seem a little desperate to me. I'm a pretty hardcore D&D player but even I won't pay $30 for a book just about adventuring in ice and snow, or any other single climate. I would pay $30 or $40 for a good hardcover revival of Planescape (or a few other older settings) done by authors who know the setting well, with good mechanics and of at least the same flavor quality as the 2e materials.
They like to market Eberron as something you can mine for materials for other games, instead of just for that setting. They could market other settings the same way, Dark Sun is desert, psionics and epic-level play; Birthright is army-scale warfare, rulership of domains, and playing nobility; Planescape is about planar travel, outsiders, elementals, and world-spanning ideological factions; Kara-Tur is a chance to do an OA for 3.5e that doesn't have any licensing agreements regarding Rokugan. Each one has significant elements that can be exported beyond its own setting.
If WotC can do one-shot campaign books like Ghostwalk (honestly, the 3e FRCS proved that you can make a very good comprehensive campaign setting in one book) or pretty limited-use and limited-audience books like Frostburn they can certainly go back to their big well of older settings and find things the fans want to buy.