I don't know that Rat has become a big consumer products franchise since its release. Are Disney Stores really still stocking Ratatouille merchandise? The reason I think we're getting a Rat ride now at Epcot almost entirely comes down to the fact that the film was a huge hit in France around the same time they desperately needed a new theme park attraction over there. Fast forward to the present, and they want to slot more IP-based rides into Epcot, have a France pavilion, and a popular ready-designed attraction based on a France-themed IP that can be easily cloned. It does seem to have proved one of the more merchandisable attractions in Paris, though, which probably has helped and I'm guessing they will sell plenty of Remy plushes and chef hats.
This is why I can't imagine them coming back to Coco in the same way 5 or 10 years down the track unless it develops a particularly strong following or an international park asks for a Coco ride and they can share the costs somehow.