Not for anything compute-intensive or serious, but for creating very secure very isolated VMs to run web apps or other services in an insecure environment. It could also be a great way to take a LAMP stack app and rapidly deploy it in certain cases.
Again not for high performance, but for... I can think of a few things personally and I'm sure others can too.
(Though honestly performance wouldn't be that bad...)
Then add the ability to go back and forth between client and server, and virtual networking, and you might have a commercial "virtual DOS LAN with nodes in a browser as a service" startup. What for? Supporting legacy DOS crap: point of sale systems, etc. "Run your legacy DOS stuff in your browser with persistence in the cloud." You'd be surprised how much legacy DOS crap is out there.