One is the "in-game" economy.
Monetizing "credit" and mineral in the GTC Market doesn't break any EULA or Licensing agreement.
Especially if its just and "exchange" between players.
For instance, credit can be transferred currently within the Guild Bank anyway.
So its no big deal, to allow this to happen on the GTC Market with "gold", real money or
something like "BitCoins".
The second dimension is the upkeep of the Server and hosting.
If the company registers as a non-profit organization, I am sure that any "income"
that comes in will not break the EULA or free GNU licensing of Dark Sky.
but you must remember, that the code is no longer the same, it has been "modified"
and with significant upgrades it most likely would not fall under the EULA anymore.
Just some thoughts.
But certainly, putting a real "value" on the in-game research, exploration, design and production which taek "real" time commitment by players would add more "realism" and excitment
to the game.