Today, I imagine the lowest barrier to entry would be to build a one-button install on one of the many PaaS's with free tiers. Heroku, DotCloud, maybe even an Amazon micro EC2 instance.
I'm proposing a button like [Create OStatus server]. It goes and provisions you a Heroku or DotCloud or Amazon account, creates an instance with everything installed, you get a link. Done.
We can make it way easier than installing Wordpress. The account provisioning part is tricky but all it takes is a good will partnership from one of the many PaaS providers, in exchange they get to upsell the owner to beefier paid servers.