Starting with saying that no work on DFW will ever start until after LAS has been released, and barring any unexpected problems we might discover *after* starting it, like missing/outdated documentation and pictures, I'd say DFW should be the next scenery that will be put into development.
This doesn't mean it would be the next scenery that will be *released* because, just as with Geneva, we have another unannounced airport scenery that has already started, and should progress at the same time with LAS, so it might be released before DFW. We'll announce this one when we'll have a better idea of a possible release date so, please, don't ask which one is. It's in the US, though...