I'd really like better linear algebra support. I've been wanting some features that have been in Mathematica now for several years. I'd really like to be able to write out,
where c is a vector and B is a matrix without having to specify their size other than they are conforming. Then be able to manipulations on them such as differentiate with respect to c. I know that Mathematica can do this, and the lack of this support makes doing my work difficult. I had to do a lot of work to get around this problem when creating my symbolic finite element package.
The other major thing that I've complained about before including in various places on Mapleprimes (but not in the suggestions forum) is better LaTeX export. I don't care about making my Maple worksheets into documents or into HTML, I need to export into LaTeX for my thesis work and for writing papers. I'm certain I'm not the only one.