This card seems weak to me. Getting to do it whenever is nice flexibility, sure, but it's less than Remodel, and Remodel isn't great to start with. Sure, this isn't terminal, that helps a lot... I am sure there will be spots of this, like develop maybe (kind of; develop is more about getting you more cards and can also straight trash coppers), it can be a role player, but I think it will be pretty weak overall.
Getting the new card right into your hand seems like it would be a big deal though. Did you miss that, or are you saying that it's still too situational?
Still too situational. Royal Seal not that much better than silver, and while this is a little better since you know what's in your hand - look, it's not like this will be AWFUL, but I still don't think it's actually strong.
As somebody who never playtested this, i predict it's much better than you think. Remodel is not only terminal, it reduces your handsize by two when you actually use it and needs to collide. This DOES reduce your handsize, but only by one, and instead improves another card in your hand. I think we learned from Tactician that one great turn is better than two mediocre ones.
As somebody who did playtest this, you are correct.
Comparisons to Band of Misfits should be made, I think. Band of Misfits becomes whatever card you need at the moment, up to $4. This turns another card in your hand into whatever you need at the moment. And instead of up to $4, it's up to X+1, where X is the cost of the card you're using as your "BoM". And then this also trashes, which is sometimes good, sometimes bad, since you'll be trashing non-junk with it.
The only real drawback is the turn it gets played. Then it's a blocked Tournament.