Sony had that, it was called OtherOS which many people used. Sony got rid, thus annoying a LOT of very talented people who were only trying to use the console for things they were legally allowed to do at the time Sony launched the PS3 with it as a selling point.
The hacks to the firmwares only came about due to Sony removing that feature.
Plus now with FW 3.60 people with the hacks can't get on to PSN and can't run new signed gmaes like Portal 2 so jobs done for Sony (for now) BUT, they will never let developers near their machine again without a fight. They are turning into an evil company and getting above MS in the the bad reputation stakes.