Or do they? Either they are language agnostic or they are not. If they are language-independent, they can't work properly, since indentation and alignment are syntax-specific (that is, need some information extracted from syntax). If they are language-specific, they can't work with all the languages I happen to need, which may include some DSLs rarely used by programmers and some languages defined by myself. I see no other option.

I have checked plugin for Vim; it doesn't work as you advertise. It either puts only spaces or only tabs at the beginning of the line, depending on expandtab setting. I assume from your comment that others work as well as this one.