I think Shrek stopped being a major franchise a long time ago, and as you said, much of its traffic is due to its location. While Pets doesn't come close to reaching Shrek's peak of cultural relevance, it really wouldn't take that much for a replacement to be considered worthwhile at this point. So long as it isn't something too obscure or niche, people will still filter into the attractions at the front of the park.
That being said, it is somewhat of a shame that they don't usually repurpose previously used IPs, Kong notwithstanding, as Shrek was always a no brainer for a dark ride.