What do you mean by commercial offering? A paid version of GitHub Pages? What would you want to see in a paid offering that couldn't be baked into the current version?
If these can be added to the free version, cool! :)
Full SSL support, integrated build automation (not just for Jekyll), redirects, built-in performance optimizations, rewrite rules, proxying, fine grained HTTP header control, integration with prerender services, etc, etc...
We can also do custom plans with true DDoS mitigation.
Why not use them to present customer projects (in private repos) to your customers? As long the pages are public this is pretty often a no-go.