I had a conversation like this awhile ago and the people I discussed this with agreed it could negatively affect the market if we did a system like the one you suggested.
We believe the optimal way to implement this is to make it a credit based system, high clintz investment system, or timed freeze like 25k-100k a week so you can't just freeze all the cards you need at a fairly low price and have to be more selective on who to invest in.. This is in order to reduce negative effects on the market when those cards drop in price due to reduced demand, but it would not start a total semi evo market collapse. For those who can't freeze their cards will also have access to slightly lower priced semi evos to maintain the current system and sellers will suffer minor losses as opposed to large losses over night since no one will need more than 1 semi evo killing most of the semi evo demand. Although more serious players will have to pay more than casuals, sellers and collectors they will also be able to benefit the most from this so they can focus on the game with their perfect team instead of having to deal with the headache of semi evos.
We also believed once frozen the cards cannot be sold until unfrozen, the reason for this is so we don't create a niche sub market where people pay credits and sell the stopped semi evo card at a premium to other players for clintz.
@anzboy I play a lot of already and I don't even really have a problem with semi evos leveling up that much... it's just a nuisance that ONE DAY it will level up so i have to buy a few. So if its a timed freeze no one would buy it.
Just think that there needs to be new changes to the game, it can get stale.
It has already been said but it really is more than just selling the cards and buying them back! It takes FOREVER to sell a card, especially a mythical. If you want it to go a bit faster you'd have to lower the price to the point you're selling a full at or below the level of a 0xp, and even so it might take too long... The market isn't healthy enough to do that.
Plus, the tax: at the very least you're losing 35k everytime you sell a 1M card, and Dregn is slightly more than that, meaning you lose even more. After 4 copies the price difference goes in the negative, and that's assuming you COULD sell and rebuy that fast, which you can't.
What usually happens is you have to buy in bulk, spending millions over millions of clintz, and then have a hard time selling them... It's not that it's impossible to do as you say, and not buy a new one everytime, but it's just not realistic.