Good points. To me there are only three possible scenarios here.
1. GoTG is clear the Disney to use and that won't change in 2018.
2. Disney has worked this out with Uni and can use the characters.
3. All the rumors of a GoTG ride coming to WDW are 100% BS, because I doubt Disney would have gotten as far as rumored without first being sure they have the rights.
I'd like to suggest one more possibility here that might fit:
4. GoTG is clear for Disney to use and that won't change in 2018, but they can't advertise or promote it
From the contract:
If the particular character is not used by MCA, such character will not be advertised or promoted by means of (x) spot television buys, billboards, personal appearances, or print advertisements which are (y) viewed, located or primarily directed to persons within 300 miles of Orlando. In other words, regional (i.e. covering a multi-state geographic region) or national television or print media buys, or brochures would not be prohibited within such 300 mile radius.
I don't recall seeing any official Disney ads for any of the Marvel stuff they have done over the last few years - Strange M&G, groot/starloard M&G, dhs movie previews, dhs Movie Magic. It seems like Disney is relying on bloggers and word of mouth for these things to get out and are not officially promoting them.
Would Disney be willing to spend a few hundred million dollars on an attraction and not advertise locally for it? No Billboards, No tourist magazines, No hotel lobby ads, No local television buys etc.
It seems like this this would be a part of the contract that could be easily renegotiated or amended between the two parties if Universal was willing, but if they aren't I don't know how Disney could justify spending E-Ticket money and not be allowed to fully market it.