6 BTC would cover all of my time for a full month, allow for budget of resources, and allow to tip the people who help.
In some places in the world 6 BTC in a month is a very good salary. Is this going to be setting a precedent? Will another 6 BTC be required for development next month etc etc.
I am not saying that you (the developer) are not doing great work with Bitmark, but I do think this is potentially a dangerous path. Should the reward not be in the projects success?