MM, I think what you are proposing would discourage participation and lure people away from the site altogether.
Because there's so much traffic here, so many new posts every day, the GBs that are not as 'wealthy' in terms of members and posts, yet remain active, will quickly disappear into page 3, 4 or worse. How often do you go to page 3, 6 or 9 of any particular forum?
If not seen, they'll soon be forgotten, and will only re-appera every other day (if you are lucky) for a quick 'breather' at the top before disappearing again quickly due to the high number of unrelated posts. Again as an example, I'll take the (my) Aerobatic Team GB, or the French Armor pre-1940 GB (to which I participate), both of them featuring new posts only occasionaly. At least in the Forum GB, they'll stay within the first two pages; put back into their genre forums, they'll disappear.
However, in the Armor and particularly the aircraft forum, the first page would still remain littered (it's not a good word, really!) with very active GBs, such as the 1/35 Tiger GB or the Pz II GB, the Pz I GB, the F-14 GB,... You'll surely remember the fuss we had not that long ago when GBs were basically the only thing one could see on first pages. Sticky or not, there are a fairly large numbers of GB that will remain at or very near to the top for months at a time (remember too that a GB such as the PzI GB is not starting until the summer, yet it's been featuring a the top of the Armor GB since its creation a few weeks ago... So for those who do not like or are not interested in, say German armor, it's not going to be a pleasant sight every time they log in...
Separate GB forums for each or nearly each genre is a decent solution, but for the sake of conviviality, camaradeship and open-mindedness, surely, a single GB Forum can't be beaten!
Even if we went ahead with only a couple of new Aircraft GB and AFV GB forums, how long before we have Helicopter modelers requesting their own GB Forum (as they did with the helico forum when it was split from the Aircraft forum)..? Potentially, that's a large number of new forums... You'll soon need two screens to see them all in one go!