It is not unusual for a company to release source code of a commercial product for an additional license fee.
Mindscape for example does it for their product LightSpeed
Whether or not this is a sensible thing to do for a compony or individual developer, depends (amongst other things) on how innovative the product is and how difficult it is to reproduce key features of the product without the source code.
I think that SublimeText contains several key features (the user interface, multi platform support, etc.) that are fairly unique and very difficult to recreate for the average software developer. Hence, its source code would be quite valuable.
So I don't expect that SublimeText's source code will be released. At least not for an affordable fee.