I love what you are doing, so don't get me wrong but it's just a declaration of intent and not binding. Also, not being open source can make people question where actually the speed difference comes from. Did you trade stability with speed? A shortcut for a common operation? Who knows!
Yet this is just a declaration for now, we do not have any intention to keep it closed source. There is no need to trade stability with speed since most of the 'current' performance difference with JXcore comes from less amount of JS <-> native switches and better memory management. Very soon we will be open sourcing it! Thanks