Halo's Finale....best to be ending now on a high note.
Extending the Halo trilogy was considered, but did not prevail. Bungie's writers thought about it since the ending of Halo 3 left an opening for an extension, but in the end the idea didn't make it past pre-production. Bungie's Brian Jarrard explains it wasn't in their best interest to continue on. So they are leaving it as the Halo trilogy instead of opening new doors and carrying the baggage of continuing on. Follow the link below to the article..