Well, I have NO experience writing that sort of software. And it would be a huge waste of time imho.

But that DOES give me an idea. Maya is very modular in design, and it's not too difficult to write plug-ins for as I understand. So it seems probable that a small team could write a Maya plug-in for building 3DGS world with all of these features. Then it could export straight to engine formats, and tighten the workflow pipeline even further. I know there is one tool similar to this out there, but it doesn't have these features, and I've never heard a review of it. Maybe it could be a good starting point if it's author wanted to further its development though. It would also be great to have an integrated shader editor in it, which would let you work with things like terrain multi tex while you're painting terrain and doing other things. That would be like the ultimate tool if it also had a good water editing system.

Maybe I should contact the person who wrote the other Maya plug-in, and see if they'd be interested in spurring it on. Would be great to turn it into an open-source project for the whole community (and be FREE).

Only downside is that it would take a long time, and I fear that we don't have that time to wait.