I don’t think Drafts replaces OmniFocus but it certainly could be your only text editor.
There’s a good question here about the apps one really needs.
With the right actions installed Drafts could certainly do a lot. And if all you need is basic to-do lists then sure, you don’t need OmniFocus at all.
Drafts can be how you send almost all text based content. Emails, text messages, tweets could all come from Drafts. You’d only need to open those apps to read incoming stuff.
You can also begin web searches in Drafts.
I wonder… could I have a home screen with only Drafts and a handful of other apps that I use as starting points? And then have home screen two for the consumption stuff?