If you can address those points, that that would make a lot of things clear to not only me, but also to other aspiring authors.
I can address some of it.
First, the single greatest obstacle is just reality. FFE is really just a one man operation with Marc being just one busy person. There are a lot of people who have a lot of ideas to do something and most go nowhere. So time is an enemy. That just is what it is.
That said, a lot depends on what you want to do. I have a friend who wants to write a book (young adult fiction). He sent an e-mail to Marc at the FFE gmail account and got a response with some simple conditions. An acknowledgement to protect the Traveller Trademark and a no rated-R content. That was it to write a book set an an alternate Traveller Universe.
The process would be harder for an official Traveller universe fiction book, because your Traveller facts would need to be checked by somebody. Remember, that means a part time volunteer.
A T5 adventure, would probably be the easiest thing to get approved at this point, because you only have Marc and FFE to deal with. However, the rules are undergoing a revision and the setting (some date in the future of the Imperium) has yet to be presented. So you would have some challenges there.
Now I have communicated a time or two with Matt (of Mongoose) and he seemed open to discussing the possibility of granting a sub-license to create a MgT product if you had something that didn't fit the standard license. I decided that for me, the investment in time to become a publisher was not worth the profits. Others have decided differently.
The 400 pond gorilla, is that Mongoose is the only one that I know of that would buy products and handle the rest of the publishing process. That is what they do with MJD (to the best of my knowledge). They pay a writer to write and add artwork and layout in-house. So whatever you want to create, you will need to sell it yourself, getting into the self-publishing business.
If you just wanted to write and get paid, Mongoose has a magazine that buys articles and Imperial-lines published articles for T5. Mongoose also has the TAS license (read carefully).
If you REALLY want a license to publish for T5, then treat it like a business. Come up with a short pitch for a proposed product and a plan to self publish it. Then contact FFE at gmail with your pitch and PM the Administrators here. They can flag your PM for Marc to read. If Marc gives you a thumbs up to proceed, then create a first draft of the product and a license. However, as a business, rather than a game, do your homework and have some idea what the costs will be. In short, convince Marc that you are the 1 in 100 that will actually produce something, not one of the 99 who just has an idea that will go nowhere.
Frankly, if it isn't Traveller IP material, it can be published under the OGL and does not need a Traveller License from Marc. So it really depends on what you want to do. I made splat books of weapons and ships. If I wanted to do so again, I would use the OGL until the revision to T5 came out or just contact Marc if I really wanted to do T5 stuff and plan on a data revision when the rules come out. Although I think places and mini-adventures are what is really in short supply at the moment. Something like the old Amber Zones from the early Magazines or the mini dungeons from Dragon Magazine (only for Traveller).
That's general data.