First you say this:
Personally, I hope Drain gets restricted the next time around.
Then you say this:
Vintage deck diversity... The thought thrills me so!
I must have missed something, how would restricting Mana Drain lead to deck diversity? Take a look at your average Tezz deck, it looks like a Highlander deck as it is.
If Tezz becomes worse, it effectively makes other decks better,
since they have to compete against Tezz.
So, if restricting Mana Drain drops Tezz's power level,
it could make decks be more viable choices to play.
If other decks become more viable choices to play,
then people might play them more often.
If people start playing decks that aren't Tezz more often,
then there could be more deck diversity.
I am aware that Tezz already looks like a Highlander deck as it is.
However, most Tezz decks do play multiple Mana Drain.
A lot of Tezz decks play a full playset of Mana Drain.
Restricting Mana Drain will probably not make Tezz less of a Highlander deck.
But if restricting Mana Drain forces Tezz players to play cards that are less powerful than Mana Drain as a result,
this could make Tezz a weaker deck overall.
This could lead to more deck diversity, for the reasons listed in the last paragraph.
I do not know exactly how much difference restricting Mana Drain will make in Tezz's power level.
In my opinion, I think after such a restriction Tezz will still be dominant.
However, I do think that Tezz will be less dominant without access to multiple Mana Drain.
If Tezz becomes less dominant than it is now, it could lead to greater deck diversity.
