Liam said in another post about this trading thing that there could be some ''cheating'' if a player trading system was implemented, even if there was a lvl cap it still wouldn't stop stuff like buying fighters with real money from other players.
And considering what Kokonut said:
I think the trading system the game could have is an event that appears from time to time and features random trading options with different requirements like 1 Dragon Brawler for 3 Wulfbanes. I already deatailed this idea a little bit more in this post if you want to read it
http://forum.skullgirlsmobile.com/threads/idea-fighter-trading-shop.3047/
I think this is a good idea. Personally I would like to see this happen. But let's put ourselves in the devs' shoes and do the math to see how we could make this profitable.
Except for some minor tweaks, updates always move in a direction that motivates players to play
more. (There are exceptions, of course, like how they changed back to the old character relic stats) Let's use your example of someone wanting Dragon Brawler.
Since there are 3 golds, the current rng of getting DB from a 10+1 Beo's relic is 10%+ 2.3%= 12.3% Thus in order to get a DB the average player would have to buy approx 16000 theo worth of relics. If a player playes consistantly to get 60 theos every day, they would have to play for 267 days on everage!
Whereas if one were aware that one would be able to one day, trade off 3 Wulfbane for a Dragon Brawler they would have to play for only 9 days in pf. This, needless to say, is too significantly bigger than the previous stats to be viable.
Thus, if trading were to exist, unless the devs are going to ask for more than 89 Wulfsbane...lol, characters should only have to be purchasable with only non-pf characters. 3 Weekends or 30 Number Ones for 1 DB or Wulfsbane and such. Good! But seeing how the reason ppl are clamouring for a trading system is because they have multiple pf characters, this is quite a bit less exciting. Also, this is less of a trading system than a 'store', since there are strict price tags, and since the devs said a store is actually in the making, with characters being purchasable with theonite, I don't see how this system would be of any immediate interest to the devs.
Anyway, that's it for my rambling. I could be wrong, or course. I can't presume to know what the devs will or will not make.