There are some rumors about a Masterverse Playset going on for SDCC...

 It's most likely a Castle Grayskull and after the MOTUC Castle, they'd need to make something far more outrageous to make MOTUC collectors get the new castle. I don't think they'd make Snake Mountain, since the KEY MOTU PLAYSET is Castle Grayskull. This means that Mattel somehow has to:

-Make a more impressive Grayskull than MOTUC to entice MOTUC Collectors.

-Make it more affordable than the MOTUC Grayskull, since it's possible that it would reach retail... and to entice those who passed on MOTUC Grayskull.

Mattel could also "reissue the MOTUC Castle Grayskull" with some modifications to accommodate the Masterverse figures. Roughly a year ago I ranted about a hypothetical Revelation Grayskull/Hall of Wisdom playset. That could also be an option, but knowing Mattel, their first playset WILL BE Grayskull. 

I would rather have an Eternos Palace, since I already have Grayskull and Snake Mountain, but Mattel won't do Eternos for Masterverse or any line. But this is a rumor and it must be taken with a grain of salt.