I can't use Mellel for serious writing in my field because support for common requirements of technical writers is still lacking. A short list is:

(1) Mentions allowed in body text so that figures, tables, equations, etc. can be auto-numbered wherever they are mentioned.

(2) Baseline adjustment for equations pasted from other programs. I worked with the folks at Math Magic and I think they've done their part.

(3) A bit of automatic layout of figure graphics, e.g., a figure goes to the top of the page where it is first mentioned unless it causes the mention itself to get shoved to the next page, in which case the figure goes on the next page.

I'm still looking for a word processor that approximates the late, great Fullwrite Professional on which I did my Ph.D. dissertation around 1990, and it did all of this and more with ease.