Just my 2 cents, but here we go...
Well let's see.... most Dark will run regular Sableye now, which still walls Mega Medi, so I don't see how that's a point.
I don't see how banning Sablenite helps the other types rise in usage, for example types like Electric were brought up. Electric still gets completely walled by Dragon, which is about as used as Dark. Poison was brought up, but it also gets walled by Dragon, and also by Steel.
It was brought up that a ban of Sablenite will cause an increase in Poison, which will affect Flying, since Poison has pokes that are effective against Flying, such as Nidoking and Nidoqueen. This is true, if the rise in Poison was to happen. But, as I mentioned above, Poison still gets walled by some of the most common types such as Steel and Dragon.
It was brought up that Psychic will drop in usage since Dark will use more threatening megas to it. This is pretty much the only thing I agree with, but only to a certain extent. With the ban of Sablenite, I expect Dark to fall in usage, since its best mega got banned.
Overall, the way I see it, some types that needed to have a Mega Sable check will now have a more viable set on their pokes, such as no Clear Smog on Weezing, and no Toxic on Mega Amph. Will that make them rise in usage? No, not really.