Thanks for the idea.
To deal with the matter, we need to do:
estimate the advantages/disadvantages of the 4 backends to select the best one as the default.
I've selected V8 for now because I had a hunch that its JIT compilation is a good way to make fast the image multi-creation (without actual measure so it should be properly evaluated).
modularize and standardize the source code to switch the backend by feature.
This is a little hard work to deal with right now so this Issue may be a long.
V8 is a quite heavy dependency, it would make sense to explore other backends to run MathJax in: