IF HBO were involved in anything, we wouldn't see anything until the next season. It's obvious from watching this current season, produced before HBO was involved, these major changes were SW's and SW's alone, and would probably have happened if the show was still PBS exclusive.
The cast was already whittled down to Alan, Chris, and Suki when this season started. Some of the changes feel like they've been in the works for some time. Especially the half hour runtime of the show, that's what the shortened afternoon version of the show was for. To test market if they can run the show at half capacity. For the record, it's a mixed bag for me. A full hour is full of so much filler, a half hour runs too fast and clumsy. The focus on a smaller group of Muppets pretty much came out of the blue, considering the last full hour season focused mostly on fairy tale characters with the main characters playing second fiddle.
If HBO had full run of the show, the changes would be much more invasive. probably replace the entire cast with B-list celebrities or something.