It looks like browsers basically all support SNI now, but unfortunately it also looks like that if you require SNI, you'll be giving up traffic from a fair number of RSS readers and search engine spiders, which makes this a non-starter for me. I'm surprised the author is OK giving up those 263 NewsBlur subscribers. I hope these RSS readers and spiders get fixed soon.

I don't think there's a point trying to send back an error document to clients that don't support SNI, since the client will get a certificate error before seeing any error that you send it. On the other hand, the clients that don't support SNI also look like just the type of clients that don't properly check certificates. If that's true, you're better off winging it without SSLStrictSNIVHostCheck and hoping that these old clients will ignore the certificate error and then be routed to the correct vhost anyways via the Host: header.