Among others they previously announced as being converted to MPEG4 sometime after April 15, 2013 are:
ES.TV
558 HBO Family 906
ESPN Goal Line/Buzzer Beater
571 HBO Family (West) 907
Tennis Channel
592 HBO Latino 912
World Fishing Network
597 HBO Latino West 913
Cars.TV
599 MoreMax (West) 923
Pets.TV
633 Action Max 924
MyDestination.TV
674 Thriller Max 926
Recipe.TV
676 W Max 928
Comedy.TV
695 At Max 929
MGM HD
744 ESPN 3D 1002
Because they ran low on equipment in the exchange programming they delayed the conversion, but may be close to doing so now. ESPN 3d itself has announced they plan to shutdown, so that one may not occur.
They have been adding additional channels, mostly sports channels and some foreign language channels, as mpeg4. It is expected that any new premium, sports, or channels in the Ultimate package only, will only be added as MPEG-4 channels. The above mentioned channels leave them some room to add additional channels, probably all to be added as MPEG-4.