Indeed, I too am a bit puzzled as to how troff and tex will fit into
things. In brief, I note that although page 27 mentions that text-plus
can have subtype troff, TeX, and PostScript, the BNF doesn't mention
them. Nor is there a section 7.3.x which defines them.
For troff, you not only need to know what macro package to use, but also
what preprocessors (e.g., tbl, eqn, pic).
For TeX, there are two major styles: plain and LaTeX.
For PostScript, I can't think of any other parameterization that is necessary.
But, PostScript also appears as image/postscript.
So, there are two issues:
1. If someone thinks that having troff&TeX are important, they'd better
write some text spelling out the details.
2. Someone had better decide how text-plus/postscript differs from
image/postscript.
/mtr