Just to make sure: "any official boards" translates into "the boards of ADB and Mongoose only" and does not cover any other boards, so there will
not be any attempt at a "cease and desist" if someone puts up his version
of a Borg cube for Prime Directive Traveller on another board ?
If there is, it would come to you directly; a.n.other forum that you create yourself in the stinking mire of the internet is just that, yours.
You might be asked to take stuff down, especially if you are essentially putting up rulebooks, but that has nothing to do with ADB or Mongoose.
This forum, however, is Mongoose's own forum and as such they are (and justifiably so) expected to maintain a degree of control over what goes on here.
A similar escapade occured in the Babylon 5 A Call To Arms forum, where one regular poster started posting up ship concepts (fine) then posting his own scratchbuilds (fine in that case) then started selling them (a violation of the B5 IP, so mongoose had to swat it or risk losing the license).
Essentially, whatever the law says, this forum will always be seen by another company as something akin to a Signs & Portents letters page; anything on here should arguably have been vetted by Mongoose to protect the general public from IP violations, obscenity and spam.
Mongoose is a company whose current commercial success is mostly dependent on its licensed IP (Traveller, Fading Suns, SFB, 2000AD, Paranoia, etc) and anything which impacts its perceived fitness to hold those could kill the company as certainly as a bomb going off in central Swindon*.
How defensible punishing a company is for things like this is is open to question but I'd rather that question not get asked!
* Lets face it, how could you tell unless you were there at the time?