As for me, you can pry my Emacs from my cold, dead fingers.
I do understand the concern though, but for a lot of people (myself included) ST is a better solution than a non-proprietary solution.
Step 1. Remove nag message. Step 2. Release to the world. Day 3. Tonnes of people jump to non-nag version and never pay.
The plugin system and API is available for those that wish to complement or extend the editor. Making the code available directly harms their ability to make money and their ability to continue to invest time and money building the product.
Perhaps the wrong place for flaimbait.... I apologize ahead of time!
And if you work in a big company, who knows! They might already have a group license you can you.
I would have bought it if it was $29 and proprietary OR $70 opensource donation ware or $49 proprietary with 3 free version upgrades. That's my comfort feel around editors - YFMV of course.