It would be great if we could have theme's selected on a per syntax basis. I really like having a different theme for different types of work, eg markdown vs php programming.

Open two files side-by-side and compare (highlight)

 IE, when you double-click "<table>" then right-click, you can choose "select tag" which will highlight all text between <table> ... and ... </table>.  And same idea, but "collapse tag" option.

Why no simple Save As dialog?  Let me save my files exactly where I want to put them.

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.

I use github and it would be great if there was git integrated into the application. I can wait until after regular expression find/replace is integrated. Until then SourceTree works just fine.

Would be really nice to have the functionality to autocomplete also custom functions. e.g. all included files or all opened files. 

Also Thank you for your work. It's really a beautiful editor for a nice price!

This APP really needs FTP support to open and edit files from an FTP storage location, without it i cannot edit websites directly which creates much pain.

A Markdown Preview like VS Code.