(Sorry for the late answer, and please excuse this off-topic digression)
MathML: I love it, but its use is not 100% reliable. I bumped on two issues:
– browser not displaying MathML (or not at all), e.g. latest version of Chrome, which is widely used. A matrix will then a appear as line vector, therefore confusing the student,
– globally good behavior with a few glitches, e.g. $\mathbb{R}^3$ displayed as ${}^3$ with no R ; unsettling again.
Moreover, we use WIMS inside Moodle (which btw does not display MathML, though it is in theory possible to have it). It has lots of benefits, such as id authentification, grading, etc. but with a few downsides: the user cannot switch between MathML and image display for instance.
Admittedly, these are technical issues, with probable solutions. My point within this discussion, was just that the grading should be forgiving for « typos » or mistakenly understood displays.