I know I've seen discussion of this before, and that the Planescape IP can generally be used for personal projects with no worries. But I found a page, http://www.trademarkia.com/planescape-74269620.html , which made me curious. Maybe I'm reading this incorrectly, but does this say the trademark is abandoned? Would that mean it's up for grabs? I was tossing around the idea of creating Planescape IF (interactive fiction) on StoryNexus, which also allows you options to make money off your project. I may go ahead with the project anyways, for free, but I can devote so much more time to a project if there is even the chance of return on time invested. If the trademark is still tied up with WOTC there's little chance of that happening, but if the trademark is up for grabs... If someone more community minded were to grab it maybe more efforts could be made to keep Planescape alive and expanding.
Planescape Trademark
IIRC trademarks are based on an identifying icon for a product (like the LoP's face and blades). Copyright apply to all the intellectual property stuff. As far as I know, WotC still owns all the PS copyrights. I may be completely off base, but I think that all the lapsed TM thing does is allow somebody else to use a similar looking face and blades (for example) in their own product identity. It doesn't allow them to use the Planescape name or in any other way invoke the Planescape IP.
WotC owns it all. We can only use the Plaescape IP due to our special arrangement with them.
DungeonMasterLoki aka George Williams
Planewalker Manager - If you have questions get in touch!
Facebook - http://www.facebook.com/OfficialPlanescape
Twitter - http://twitter.com/planewalker
Google Plus - https://plus.google.com/communities/114763908734601085075
Dungeon Master of the Planejammer Campaign Series , Celebrating over 30 years!
https://planejammer-setting.obsidianportal.com/
I'm not 100% sure, but I think you're confusing trademarks and copyrights. You might be able to name a product Planescape, but I don't think you'd be able to use any of the actual Planescape material.