It's not that Tribes: Ascend won't come to Xbox Live Arcade ever, it's just not happening soon.
When Global Agenda developer Hi-Rez announced its Tribes reboot, Tribes: Ascend, it was coming to both PC and Xbox Live Arcade sometime this year. Though a console version could still happen, GameSpot UK's reporting the studio has turned its focus to the PC version for the time being.
"An eventual XBLA version--and even PSN version--is not out of the question but neither will be this year," said the company.
Part of the decision may be attributed to transforming Tribes: Ascend into a free-to-play game. There have been rumors of Microsoft working to enable free-to-play experiences on Xbox Live, but so far, that hasn't come to pass.