It's hard to mess with Mechwarper's cost or stats. Any change would have to be to the mechanic, so if they do nerf it, I'd expect it to get the Summoning Portal or Pint-Sized criterion. It could also be made so that two Mechwarpers don't stack their effect.

Mech mage is strong but relies completely on early tempo and board control, and it's actually a pretty precarious balance. If the deck hasn't won by turn 7 or 8, it's usually a loss because there's no lategame, and if you can't secure board control pretty early on, the deck completely collapses as soon as your hand is empty. It has no draw, usually can't rush you down as fast as face hunter, and kind of relies on the exceedingly fragile Antonidas combo to beat control decks if you don't get that dream starting hand.

As such, screwing with the mana curve or board control potential leads to a disproportionately severe nerf to the deck as a whole. The problem isn't that it costs 2 mana or has 3 health, none of the problems result from its stats. The one and only issue with Mech Warper is that the cost-reducing effect stacks and applies unlimited times per turn.

The deck can't really afford to be much slower or have a weaker board control. It already has a 40/60 disadvantage against some of the most common decks, and doesn't have any matchups that it completely dominates. It's just that it has no real achilles heel either the way control mage decks auto-lose against warrior.

People overestimate mech mage because it's so popular, concluding that it must be grotesquely overpowered because everyone plays it. The reason everyone plays it is because it's one of the only affordable top tier decks whereas most of the other top decks cost four or five times as much. For a newish player who plays arena for a month or invests €100 into the game, mech mage is usually the only great deck they can make at that kind of price.

A nerf to Dr. Boom is practically certain at some point, and this will hit mech mage slightly harder than other decks as well due to its minor synergy with the mech bombs. It's also a relatively new deck, in a new meta, so things might look different once its counters are established. It's not so overpowered that a significant nerf is required, let alone urgent.