Your comments

Oh, and you can select XML syntax highlighting for SVG files by manually choosing it in the "File Information" popover for now.
If it doesn't work for you in Textastic 1.1 then it's probably the same issue as with php files: see http://feedback.textasticapp.com/feedback/8060-web-preview-of-php-files-doesnt-interpret-html-part/ – I've fixed this in Textastic 2.0 which is currently in review at Apple.

I'll add the svg extension to the XML syntax definition for a future version.
Thanks - and the German was nearly perfect, danke ;)
The article at http://stackoverflow.com/questions/2936326/what-is-the-difference-between-erb-rhtml-and-html-erb seems to confirm that.

I've added the erb extension to the rhtml syntax definition.
I've added a "Read-Only" editor setting to the app's settings.
I implemented #2 for Textastic 2.0 because I could use the same interface as for the FTP client.
This is implemented for Textastic 2.0:

I added a "Move" button next to the "Delete" button that will allow you to move files and folders to other folders.

It's also be possible to rename and copy files and folders.
I'm not a Ruby user myself, so can you tell me more about .erb files? Which syntax highlighter should it use? HTML? Ruby?

I've just added the extension to the list of file extensions Textastic can open, but it won't be syntax highlighted yet.

The Open In... dialog is provided by the system. Actually, Dropbox has to tell the system which files it supports, so it's up to them to add this to their app.

But, Textastic 2.0 will have a built-in Dropbox client, so this shouldn't be a problem anymore.