I've got a few games in my Steam library now, and I got a free copy of Watch Dogs with two of my new graphics cards.
I'm interested to find out if there are any services which take one digital licence and provide you with another on a separate platform for a service fee or such.
 
Even though trading isn't permitted once activated - I haven't found anything like it or anybody asking the same question.
Does anybody know if such a service exists?

 You can sell your keys for credit to buy other keys, https://www.g2a.com/ it's a lot easier than trding, as you don't have to look for the people to trade with and there's a much lower chance of getting scammed as you never talk to the peron who buys your key.
 Currently they do have Watch_Dogs Steam keys[nevermind there was only one and it just sold], but heavily marked up and not worth it. That's because you actually have to contact the developer[on the steam forum] to order keys, which it is hard to get direct to consumer keys, unless you order bulk, they really do want you to use Uplay...  
Watch Dogs Uplay is selling for 21.49  [21.41 is the average listing price, the lowest is 13]
I've heard WatchDogs isn't very good anyways, though.