The infamous plans for a Halo movie have been in developement hell for years. Partially due to lack of production interest and funding. Not to mention video game movies have a less than stellar track record. Halo: Legends, and Halo: Faith ( a fan-film) however, show that there is enough basis and interest for a Halo movie.
A Live-action one is unlikely, given funding costs, and the resources necessary. A full theatrical release is also unlikely.
However, a CGI-based movie (think the Halo Wars cutscenes, not Legends for that) would be possible, and potentially more suitable for the Halo audience. While CGI is relatively expensive, in comparison to that required for a decent action movie, it’d preferable. No need for on-location shooting, or props or anything similar. Not to mention you can do things with CGI you cant with live-action.
In terms of actual distribution, it could be given a limited theatrical run, streamed on Waypoint for a limited time, then went direct to dvd and download.
That’s just the logistical side though. A decent movie would require a good script with actual characters, an interesting story. They’d probably need to create a new continuity for it to be any decent in terms of scale.
Just my two cents.