I really think that in spite of what we, as fans, may think are viable products for release that the metric that the band and/or record company follow is significantly different.
There are also VERY different reasons at play for what does and doesn't get released. It is VERY clear that the band really has absolutely no desire to release anything for the sake of completeness. It either meets their definition of quality or it doesn't get released, and with at least three or four members having veto power we've seen a lot of things get the axe or seemingly never be considered.
But the final arbiter really is the record company. They are the ones paying for the work and expect to see a profit on any release, and the budget set might not even quite match the amount of material the band is willing to release. That is exactly the situation with the '07-'09 boxed sets, where the white and black boxes had significantly smaller budgets because the the blue/red/green boxes had underperforming sales.
That's why I'm a little frustrated by some of the comments I've read here about the upcoming BBC box set, how many are going to skip it entirely because it doesn't quite live up to their "throw the archive doors wide open" expectations.
The way I see it is (1) many fans don't have the same exhaustive collection of bootlegs, and that official set is still a significant release, in spite of the number of "would be nice" songs that aren't in it. And (2) EVERY chance of more Genesis releases is based on how well the last Genesis release sold. So every "huge fan" that doesn't buy an official release is directly affecting how large the budget is for the next release, or even deciding if there is a next release.
Now there is a new owner of the publishing rights for the whole catalog they might be more motivated to try more releases to try to make that investment earn them some money, but I'm afraid if the more "fan friendly" releases (of which I'd put the BBC box firmly in) don't do well, we are a lot more likely to see just re-release and re-packaging of the same studio albums over and over again and fewer (if any) odd bits from the archives.