SASS / SCSS are a mission-critical part of all my agency's projects, and many, many others. Currently, we use PHPStorm as our main web development IDE (which has native SCSS support) and Sublime as our "quick editor" (requires a plugin for SCSS support).
Aside from the usual web technologies (PHP, JS, CSS, HTML, etc) one thing we would really, really need Textastic to support is SCSS. Currently, Textastic for iOS doesn't have this support (which is a tremendous shame), but will you be including support the OSX version?
As far as I know, no other "basic editors" have native, built-in, out-of-the-box SCSS support. Include this, and I'm sold.
Customer support service by UserEcho