IMHO I'd say "be careful what you wish for". Open Sourcing an active and thoughtful project could lead to enormous confusion. Open Sourcing works where the path is unclear, which is not the case with Sublime. As a paying user of Sublime, I am more than happy with the chosen path, and have found myself trusting the decisions made, the pace of innovation, and the quietly considered and absolute reference point. I cannot say the same for many "plugins" I have tried, which are somewhat arbitrary and often not well thought through. So I'd say, keep it closed source. Consider that the benefits of this editor far exceed the modest payment required to register.