It sounds reasonable, but if they diversified quality, it would mean making precision glass and then also somewhat less precise glass. They will not start mass producing large panes of low margin glass. It's not what they're good at and it's not a lucrative market. Like Intel isn't going to start making jellybean parts.

They could license their name to some existing glass company, but they still wouldn't really be the ones producing it, and I think Zeiss has avoided diluting their brand name like this so far.

I doubt Zeiss makes their own glass. Most optics companies outsource that to one of the big glass fabs: Schott, Ohara, CDGM.