The UD5007 is a discontinued item. Unfortunately, Marantz has no control over how or when Youtube/Hulu/etc. change their streaming protocols. It's not in any company's best interest to continue to redevelop firmware on discontinued products to keep up with changing technologies (since they are no longer selling that product). Even Oppo is getting out of the streaming business with their latest 20x series players.
Your best bet is probably to get either the Amazon FireTV unit or a Roku. Both Amazon and Roku are in the business of supporting many streaming services and this will keep you current on any changing or new technologies. The Amazon Fire has a very high quality app for Youtube (both high quality video and audio transfer).