Microsoft has always talked about the support of this feature for disc-based titles, but it has not yet confirmed support using this feature for Xbox Live Arcade or to download title offerings. Sony has already confirmed earlier this year that they, too, will support partial-download play.
At one point, a rumor was circulating that Microsoft was looking at dropping this feature, but apparently this was not correct. The questions that have gone unanswered are surrounding download titles.
Read more here.