A shower thought which applies not specifically to MTG, as it would obviously be a different game.
What problem does this idea try to solve?
Balancing. It is hard to balance every card during design phase (or even impossible, as can be shown), which results in some overpowered cards which make the game less fair.
How?
Supply and demand. A card which is played often (by many players, in many games) has it's mana cost increased slightly. A card which is played rarely becomes cheaper.
Implications
This is probably not feasible with most mana costs sitting in the 1-digit-range. We can't make a 2-cost card "slightly" cheaper. So we would either need a mana system which works with decimals (e.g. 3.1415 CMC), or raise the integer system to a higher plateau (e.g. 314 CMC)
It's also only contemplable in digital versions, where a server can monitor every card drop, and adjust costs accordingly.
A big drawback is that your deck's costs can change over night (or even between consecutive games), forcing players to edit their decks more frequently. A partial solution could be a notification system, and/or scheduling the recalculations to a slower frequency, like once per week or once per month.
A big advantage is that we now have an impartial Big Brother watching the balancing. Humans can err, crowds and echo chambers even more so. When people complain about an imbalanced card, is their cause justified or is it just a small but loud minority? Monitoring the cold hard data seems like a better way, and automated problem solving likewise.
What are your thoughts on this idea? Do you know another TCG which applies something similar?
I was struggling to figure out how to express another problem, but I just thought of how to say it. This deeply entrenches metagaming into the game's formats, since competitive players will even more greatly want to keep secret strategies in their pockets so the wider scene only finds out after they've already reaped the benefits.
Basically, it's the Magic version of arbitrage. Everyone in Modern is sleeping on Séance, so you keep quiet about your Séance brew until it's Pro Tour time and you get to cheese wins with an undercosted Séance.
Tangent time! During Pro Tour Amonkhet, there was a cheesy WU snake deck in draft. Some of the competitors expected Slither Blade to be badly underpicked, so forced decks full of those and Trials of Solidarity. It worked. Once this archetype went public, it stopped working because people were actually trying to pick that snake now. As far as I know, there was no other deck for Slither Blade, so this was basically insider metagame trading.
Okay, okay, paragraphs. I know you said this was about more than just Magic, but I don't have enough confidence in my game design or macroeconomics knowledge to say anything insightful in that regard. I mean, some board games have auctions.