This mechanic feels like it has a lot of potential! There's a lot it can achieve that Durations or Reserves can't, whilst the timed aspect distinguishes it from Exile.
One snag I remember being discussed is the sheer number of tokens potentially needed; even if dice were used instead of tokens, there is still a large amount of freezing potential to account for. I think the best solution reached was a
Freeze mat, with spaces on it forming a countdown track? 'Freeze X times' would mean put the card (set it aside) on the relevant space on the mat. All you'd have to do is shunt the piles on each space along at the start of each turn. It would imply a limit to the number of times cards could be frozen, but that's probably for the best.
IMPORTANT NOTE: I think the ice token mechanic is overall fine. The only problem is that it discards cards at the beginning of your turn. That means the first ice token doesn't do much (instead discarding at the end of your turn, you discard at the beginning of your next, which usually doesn't make too much of a difference). The other big problem is that it cause cards to miss the shuffle. With this card in particular (with the original rules as is) it's hard to make it work no matter how many ice tokens you put on it:
1 ice token: Can have infinite loops
2 ice tokens (my original thought): If you have a chain of them and use them to remove the other ice tokens, each will have one at the end of the turn and will come back at the beginning of your next which is pretty much a lab.
3 ice tokens (the not so great solution): Ok so add one ice token and everything's fine right? Not really. Labs tend to be in decks meant to draw your deck, thus the turn before you get them back, you likely triggered a reshuffle when drawing your starting hand, meaning frozen cards will likely go into an empty discard pile. Even if your deck was still strong enough to draw to them, it would be pointless because at that point you've already drawn all of your payload. It would have this really staggered and weak lab effect.
Solution: Ice token rule change - When you remove the last ice token from a card, discard that card at the end of that turn.
This does pretty much the same (just with one less ice token) except you get to shuffle the incoming cards into your deck, and have a chance at drawing them.
So cards 'naturally thawed' at turn start would also wait until turn end to be discarded? That would mean one Freeze keeps a card out of deck for 1-and-a-bit turns, which would affect the usefulness of something like segura's Scout heavily. You could add an extra clause to this card, 'you may thaw one of your cards once; if it's then on 0, discard it at end of turn' (to use Freeze mat terms).
On the one hand, this rule change lets thawing cards work, and freeze once is a more significant delay; on the other, it's a little more confusing, since hitting 0 implies the wait is over then. The rule could be printed on the mat though...
So, I guess I'm overall in favour of this change.
So my entry will use it too:Glaciate - Action, $3 cost.
+1 Action
Trash a card from your hand. Gain a non-Victory card costing purely $, freezing it once per $1 it costs more than the trashed card.
Remodel where the only limitation is Victory cards, but the bigger step-up in cost you go, the longer you have to wait. Trim down your deck early, ready for the power to come in later.