I'm no expert when it comes to Morelia, but from what I understand selectivity is based more on locale than morphs. There are a few carpet morphs but the different coloration in gtp's is based solely upon locale.
They definitely are becoming more popular, but I don't think they'll ever beat out ball pythons simply because they have more elaborate husbandry requirements (arboreal caging and high humidity levels) and because they aren't ideal snakes for beginner keepers and therefore there are fewer potential buyers. (Not saying this is a bad thing, imo keeping these snakes among experienced keepers is great, it just means that they don't have the same potential for popularity as ball pythons do.)
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