@mbgraham ...
Out of curiosity, is there a benefit to using this within the RCE? Your browser already has a built-in spell checker, so there's really no need to use another spell checker in another tool.
As for the grammar checker, I can see where this would be helpful. But, if you were to even copy/paste test from a Word document (I'm not sure how the Word Editor differs), sometimes there is a lot of junk code that comes along with that into Canvas content pages. Since I'm not familiar with the Microsoft Editor (which I just found here: Free Online Text Editor Software | Microsoft Editor), I don't know how it could possibly integrate with Canvas...if at all.
I know this might not be too helpful, but thought I'd add my $0.02 for you to consider.