Don't you think it would be a good idea to give users the option to use Textastic the "plain old way", i.e. save only when and where you want to?
I think that a lot of developers out there will NOT use Textastic only because the auto-save feature is something you expect from a "prose-only" text editor, not from a code editor. This is only my humble opinion indeed. 
The app has some very interesting features and is well made, this is why I've happily paid for it, but I think I will not make use  of it anymore because of the saving "issue".

Something that you can expect from every developer out there is the desire of flexibility and personalisation about his/her apps, and Textastic for Mac isn't providing much of them.

+1 for a configurable key mapping. ctrl+space would be my choice.