Why would you return your copy of skyrim o.O
But yeah, from what i've heard, some of the projects people are planning sound amazing but also sound doomed to fail due to the amount of people wanting to do their own thing. Whilst a nice big project sounds like a fun thing to do solo, eventually most people stall and abandon it or release a half arsed version

Yes this is a big problem for large mods. Often its difficult to get people to share the same vision but a big project needs to accept sometimes that people will drop in and out continuously but as long as progress is being made the mod can make it and grow quite well in the windows of greatest opportunity.
I'm glad there is a heightmap of such size as it bodes well for my mesogea mod, if I am to port across a heightmap many times larger than the Skyrim/Oblivion lands combined. The first construction kit version for Oblivion wouldnt allow heightmaps of much more than double the size of the Oblivion map. Hopefully the Skyrim CK will allow the same as the second construction set, expanding the visible LOD land etc.
There will be a massive release of lots of mods initially with a whole host of people modding their own stuff but thats useful. It adds a lot of diversity and allows for troubleshooting and snagging on a massive scale. As some people move over to the larger projects they will have cut their teeth on modding already, so I would say dont expect a great exodus to the major mods for a while, that will probably happen gradually.
I've been working on Mesogea since Oblivions early days with a break of 1 year for work reasons. Skyrim wont be half as difficult because the lions share of the work, the hundreds of custom textures and models are already done.