Check out the announcement:
The announcement comes from the December issue of JUMP SQ, where the GATE7 one-shot will be published. It says that GATE7 will be part of a "large scale project" between CLAMP and JUMP SQ. Could it be related to Dark Horse and the Mangettes?
Update: There won't be an actual signing session, instead, a paperboard with CLAMP signatures will be displayed at the event.
The color page featured in the one-shot was posted in Ritual Scan:
In other news, CLAMP member Nanase Ohkawa just recently made a post in her Private Board about getting ready for a new "location hunt" for GATE7. In the post, she goes about how she is no good with packing even though she enjoys traveling. She says that even though they did a "location hunt" earlier this year for GATE7, she will need to do it again.
It's unsure if the 3 other members will follow Ohkawa to the trip. Check out her post here.