Much as i'd love to see it, i don't see it happening with this movie. Disney's whole overarching goal is to reestablish the (Classic) Muppets as its own brand and reminding people that this family of characters is different than the Sesame Muppets is a large part of that.
The next Muppet movie, i'd say is a great possibility. But not this one. They're not going to run counterproductive to what they see as the main purpose of the film from a branding/marketing place to appease those who want to see a SST crossover akin to the cameos in the first three films. But at least they're making up for it by giving us lots of rare Muppet cameos from within the Classic Muppet family instead (and hey, if it helps - you can view Beautiful Day's presence as a SST cameo since he has history with both)
As much as lots of Muppet fans would love to see a one-line cameo from Cookie Monster, Disney's need to get the general public to be able to take kids to a Muppet movie or view a Muppet project without every six year old in the audience asking "Where's Elmo? When is Elmo coming?" (or every sixteen year old, for that matter) is greater right now.