Short list of important things it doesn't do: binomial coefficients, matrices, floor and ceiling, modular arithmetic, any letters in fancy fonts beyond blackboard Z, R, and C, and these are just all the things that I use frequently. I imagine if there were something I didn't know how to typeset, the chances that this tool would give me anything useful are close to nil.

But lack of vocabulary isn't even the largest problem. The other issue is that, unlike Detexify, this tool doesn't provide any alternatives to its best guess. Which means that unless it's made perfect (and that's not going to happen) you're going to spend a long time fiddling with your equation trying to make it work. And then you might as well learn LaTeX anyway.