- Will Triplea ever be mercenary?
Do you mean that if someone were willing to pay for the development of a feature, would that feature get higher priority or a guaranteed addition in a future release? I don't think I have the authority to answer that question, but I just want to clarify what you mean when you use the term mercenary in this context.
- Are people able to copy some Triplea features then implement them to their games?
TripleA is licensed under version 3 of the GNU General Public License (GPLv3). In a nutshell, this license permits you to redistribute or make changes to TripleA code (including copying the code into your own program) as long as you abide by the terms of the GPLv3. These terms typically require you to make your modified work also available under the terms of the GPLv3.
Let's say, for example, you have a great idea for a new set of rules that the TripleA devs cannot or will not support. You are free to fork the TripleA code and make whatever changes you like. However, if you ever decide to release your new-and-improved version to anyone but yourself, you have to follow the terms of the GPLv3. The big deal there is that you have to make the modified source code available--at no charge--to anyone who wants it. Note that "at no charge" doesn't mean you can't charge people to buy a compiled version of your game or to pay a fee to play your game online. It simply means you can't charge for access to the source code.