Happy to jump in and explain why we are not doing Castle Grayskull like we are doing the Hall of Justice in the fall 2011 YJ line.
The "Hall" is a sculpted backdrop. It is not an actual "playset". It is a plastic backdrop of the Hall's front with a pegged display in front for figures.
If we did Grayskull we would not want to just do the front as a flat sculpted display. We'd want to do it right and do a real playset.
The problem is the tooling for this would be through the roof and we just don't have the sales yet to justify this. The reason we don't want to do the Castle broken up into rooms and sections that can be built into the Castle is because that would make a difficult project (a 6" scale playset is not an easy design!) even more difficult.
Designing a bunch of smaller rooms that can interconnect and build up is just a huge amount of design work and a small line like MOTUC just does not have the resources to do something like this.
What limited resources we have are being put into the figures to make them the best they can be!
No one wants a Grayskull around here more then me. If we ever have the option to do one you bet I'll push for it.
Hope that helps.