[QuantaCondor]

This is one of those ideas that requires a large amount of devtime for a truly small payoff. Go to any other Ultimate Team gamemode with both an AH and a trading system. Which do you think gets used 99.99% of the time?

And there's a reason that in all those games with a trading system, "locked" cards are also banned from trading as well. Besides, why would the developers have any incentive to do this? It just increases supply without changing demand, which lowers the cost (and reduces their profits). It's a ton of effort for a potentially negative payoff which only has a truly niche use case for only the subset of players who want to do card trading, which is probably a smaller fraction than you think.

It doesn't make a necessarily positive impact on the economy even for those players who are interested, either. If you think silvers, golds, and diamonds on the AH are rare and that the offers are outrageous, you're going to be shocked to find out that people's valuation of these weird locked card trades will not be much different. You may as well just be asking for collections cards to not be locked, it would have nearly the same effect while being way less hassle (and more obvious that this idea is just a request for free stuff).