Given that Spearhead is already on bluray, and most of the others would need a lot of work, I doubt that season 7 is near the top of the list.
The problem is that we're nearing the end of unreleased seasons that don't need a lot of work in one way or another.
Season 1 - Rights issues for AUC, recons for Marco Polo and The Reign of Terror 4 & 5
Season 3 - Recons for Mission, Myth Makers, DMP, The Massacre, and The Savages
Season 4 - Most stories recently released as standalone animations
Season 5 - Fairly straightforward if they can use the BritBox recon of The Wheel in Space
Season 6 - Recons for The Invasion 1 & 4 and The Space Pirates
Season 7 - Further color restoration for 3/4 stories
Season 11 - New color restoration for Invasion of the Dinosaurs 1
Season 13
Season 15
Season 16
Season 21
Season 25
The Wilderness Years (TV Movie and probably other things from the interim years)
That's six sets without major issues and seven sets with "issues" of one sort or another. I would hazard a guess that they'll do one of each per year for the rest of the range (unless they manage to get back to 3 sets a year, which would be nice, in which case I'd guess they'll alternate more and less difficult seasons).
That being said, I'd guess that Seasons 1 (because of the AUC rights) and Season 4 (because of the number of individual releases, including The Smugglers, which is rumored to be the next animation) will be towards the end of the range.