It is still on my todo list but didn't make it into version 7.0. I hope I can add it into one of the next versions.

Good point, this could certainly be improved.

This is not really related to the filtering. When you open a file from the list of files, it is opened in a transient tab, indicated by the italic title. When you then tap on another file, that file replaces the transient tab.

To make a tab stay when you open another file, tap on the file title or the pin button at the right side of the transient tab, or tap on the editor to bring up the keyboard.

This behavior is very similar to what you see in desktop editors such as Sublime Text, VS Code and Atom. It prevents you from opening too many tabs when browsing the files in a project. 

If you tap on the editor in landscape on iPhone to bring up the keyboard, the blue bars should already disappear (same as in portrait). Is that not the case for you?

I think that's covered by XML.

added

added

Ok, I've added you to the TestFlight beta. You should receive an invitation by email soon.

You should already be able to use the Material color schemes in Textastic. The .tmTheme files are here: https://github.com/equinusocio/material-theme/tree/master/schemes

See https://www.textasticapp.com/v6/manual/lessons/How_can_I_add_my_own_syntax_definitions__themes_and_templates.html

In Textastic 7, the document picker ("Open…" command) will be able to open any file with any file extension, not just text files with known file extensions. Textastic will warn you if you try to open a binary file. You'll also be able to select more than one file to open them in tabs.