Thanks for giving this subject its own thread! Very exciting discussion here!
I have tried the LEGO design programs in the past and just looked at the latest version. I am simply not geeky enough (though truly I do claim some level of geekdom for myself

) to delve into them deeply enough to adapt them for Playmobil parts. Also, although I do enjoy LEGO I don't love it enough to learn the whole LEGO design thing for this purpose.
. . . I'd need help, not only on the back end, but the ability to pull in the interested public to contribute. (The emergence of collaborative media, also known as Web 2.0, makes this a much more likely option than it might have been in the past.) As long as the focus stays on helping Playmobil owners enjoy their collections and creations, it will stay fun and rewarding for me, which is pretty much the only way to guarantee my work.
The proper enquiries/inquiries will be made ... 
If Heather were on board and Richard can work his magic, I would definitely be interested in doing whatever I could to help out. (It would be a welcome change from caressing my MISB sets and wondering how much I could get for them on ebay!)
Do we want a CAD in which we create pieces from scratch, or in which we have a library of pre-designed pieces that we assemble at will?
Why not both? The library of all existing pieces would be a must, with the ability to alter colors as desired. But how many times have we all tried to build something only to discover that a particular connector or roof piece or what-have-you simply does not exist? The ability to modify existing pieces and to create new pieces would be very useful in these cases. There is so much brilliant creative energy in the Playmobil community that I can't even begin to imagine the wonderful and entirely new things people would design with this capability.
I doubt PM would ever give us that sort of support though, considering that would be a seriously adult-collector-oriented project. We'd be more likely to get a dress-up video game, with a limited selection of parts for a specific theme, to create our characters, and go through some sort of adventure.
It could be a good income source for them though - people might be inspired to order lots and lots of parts through direct service (Geobra would probably need to expand DS) and these are parts which don't have to be packaged in pretty boxes and sent out to retailers for resale. Geobra would potentially be able to sell large quantities of product directly to consumers. These would be products which enhance the retail line and which aren't directly in competition with the retail line. Geobra could also learn what new parts are desired so that they could manufacture and sell them (for example the much-desired Steck/System X connector.)
It would not only appeal to adult collectors, but to parents who like to play long with their kids (a lot of us got started that way

.) It would also appeal to kids who are older and still enjoy Playmobil but don't necessarily want to admit it

. The program should include the ability to catalog the sets and parts that one owns (as a design tool) but also to help to organize and inventory all those thousands and thousands and thousands of pieces

.
- Anne