Turns out that it is possible, albeit very challenging. This is according to the Xbox engineer head Mike Ybarra who was on the Inner Circle podcast. According to Ybarra, “We’re not looking at original Xbox games on Xbox One yet. Right now the focus is making more Xbox 360 games work. [It would be] certainly very challenging. Getting Xbox 360 games to work was incredibly challenging and really a multi-year engineering investment. Going all the way back to the original certainly would challenge the team.”
However he also adds that, “Nothing’s impossible.” Ybarra and Spencers comments should not be taken as a confirmation that there will be original Xbox backwards compatibility, just that it could possibly be in the cards in the future if that’s the road Microsoft wants to head down, but in the meantime gamers looking to relive some older games will just have to make do with Xbox 360 backwards compatible games.