I'm beginning to wonder if the back to the beginning isn't so much a force for why they didn't use Pepe, so much as a force for why they aren't all that familiar with him. Though, I still say, he single handedly saved every movie he was ever in, especially MFS.I was wondering about Pepe too. He has become one of the major Muppet stars since 'Muppets From Space' so I'm assuming he would be, but maybe you're right about this being a 'back to the beginning' thing. Though if that's the case, they ought to make a 'Sesame Street' movie without Elmo. Lol.
I don't think Elmo in Grouchland was so much a bad film because it focused entirely on Elmo, it just wasn't a great film because it felt so artificial and they added too much Elmo's World style fourth walls, disrupting the flow of the movie. If another SS movie were EVER to get made, Elmo would no doubt be in it, but I think the next one should focus on Grover (since he's had a resurgence of popularity thanks to Eric). But I doubt we're going to see Sesame Street try a legit theatrically released film in the near future.