iOS offers it's limitations to users and developers and it is unlikely that we see Apple opening their APIs and support tools like TextExpander or OmniFocus from within their own apps like Mail or Notes on the iPhone/iPad.
As a consequence simple tasks like creating an action from an email in OmniFocus becomes a little complex and annoying. While the OmniGroup offers it's Send-to-OmniFocus email service it is a band-aid at best.
A somewhat nicer approach is what Hunter Hillegas has to offer. It requires you to have a (spare) Mac running 24/7 with Mail.app and OmniFocus open. His script captures emails you flagged in Mail.app on your iOS device and turns them straight into OmniFocus tasks. OmniSync server does the rest and you find the task right in your OmniFocus inbox.