Well, Gemini can have links to pictures and clients may render pictures — inline, in separate "graphics" column etc. No one does it yet, as far as I know, but we will see.
Table and math bring more problems. Probably SVG or other images can solve them, but it is a pain for authors. In my opinion, no plain-text markup language today has tables with features even remotely close to HTML (at least colspan, rowspan and alignment) while remaining convenient to both write and read. AsciiDoc is fine in terms of features, but not in terms of syntax:
Gemtext might not be as full featured as some might like, but you can always serve markdown instead.