I doubt the contentEditable spellchecking will ever work, it seems the standard allows browsers a lot of freedom in how/when they spellcheck. Chrome seems to only spellcheck in response to user input events. Since CM sometimes redraws the text after user input it seems in those cases chrome will not spellcheck the redrawn text. I expect other browsers to give poor results as well.
I created a spellchecker with typo correction here:
https://gist.github.com/kofifus/4b2f79cadc871a29439d919692099406
Demo: Plunkr
hope this helps