Aren't you creating an artificial dichotomy? The options you imply are:

1. block all IE9+ 2. spend lots of time and money making the site perfect in IE9+

What about this?

3. Have a quick glance and if things look 95% ok, let people know it is not optimized for IE9+ via a subtle notification. (That actually requires no more developer resources than blocking IE9 explicitly)

Or:

4. Set up a VM (it isn't that hard, and you only have to do it once) and just fix the obvious big stuff (which it doesn't appear there are any). Again, very cheap.

I'm no fan of IE or MS in general. Frankly, I'm a shameless hater. But I'm just not following your logic here. I would totally buy "I block MS because MS is evil, has caused me pain in the past, and now I am exacting revenge on them".