Many years ago (I'm thinking not long after the demise of Imperium Games), I wrote Marc a letter asking him a few questions about unresolved questions in the story and whether there were going to be any more T4 or TNE books (or something along those lines), and in his reply he mentioned a "Far Far Future" in a tone that suggested that diehard fans would have heard about it (by which I assume he thought I was a diehard, since at the time, Traveller was pretty much dead). I recall him saying that Jump drive would be surpassed, and something about psionics being linked to Jumpspace, and creatures that lived in Jumpspace. (Although it's been so long and I may be confusing some of the things Dave Nilsen revealed about his own plans.)
Having just read a two-page "in-character" description of the Galaxiad, I would guess that this is what he was talking about back then. Whether any of the ideas he shared with me back then have survived or mutated, I can't say. However, I seem to recall having the impression he was talking about things THOUSANDS of years after 3I.