Making cards of people has two downsides.
First, everyone wants himself portrait.
Second, Most people don't even know the people portrait on the cards.
I recently came up with an idea I think worth describing here.
My idea is about making cards about Add-ons.
Like weapons, vehicles, tools, effects, event mods, gamemodes, and even single bricks.
You just need very creative Card creators and even cards about script are possible.
The best source for the Add-ons will be RTB.
It is more interresting to have some materalistic things to trade.
Portaits or Profile cards are just too personal and might someday get boring.
The whole cards distribution system should be automated.
Of course Admins of the Trading Cards server shall be able to give people cards but you should also be able to get to the rare cards by chance.
Also, the player should decide how much every card is worth by its look and the actual add-on it represents.
So you could get every card without the need of an admin who privileges only a very small group of players.
You know, the more a card is traded, the more common it becomes because more people have it.
Compare this:
Joe: Hey Sven, I have Hedicalking wanna trade?
Sven: Yes, what do you want in return?
Joe: Uh, what do you have?
Sven: I have Badspot, Deep2 and Kalphier for trade.
Joe: I take Kalphier.
Sven: *Trading*
Joe: Hey Sven, I have the Swiss Army Gun wann trade?
Sven: Sure, what do you want for it?
Joe: Just tell what you would like to trade.
Sven: Ok, I have Handgun, Mininuke and the 4x8 brick.
Joe: I'd like the 4x8 brick, I'm collecting all the 4x bricks. ;)
Sven: *Trading*
I could write thousand words but a picture might give you a better understanding of what I mean: