Personally, i dont really feel there should be a sale... Although, if there is to be one, they should wait til patches are at least finished.
Maybe make a 4.0 or whatever. Glacial is sufficient. Put stats on them that would balance the current ones already out(less offense/more defense).
2.0 and 3.0 are both good in their own ways. If there is a permanent sale, they should both be sold. Not just 3.0 because, in some regards, 3.0 are not ideal whereas a 2.0 upgrade would be. I've even seen a 2.5, if you will. Half 2.0, half 3.0. It was actually a pretty nice club, stat-wise.
More damage output than what is currently on 2.0/3.0's would be a mistake in my opinion. From what i see in all these patches is a huge boost in offense with only a mediocre boost in defense. It's a heavily offensive patch. A lot of one shot kills from many classes.
Option stones on IM/Game Parlor are something that would definitely need looking at and possible revision on the availability of certain ones(Perfected Wings of Silva as an example. Guaranteed 70% ele damage on upgs now is a bit extreme), if there were to be a sale as well.
The way i see it though, if player equality is the goal then do a perm sale of all upg weapon types.
If class balance is the goal, don't sell ****.