A pretty even spread of votes right now. It is possible that telltale may want to revisit this idea, but I see that new telltale titles are being revealed soon.
In Lair of the Leviathan we will have the opportunity to see more of her and I hope: have the chance to play as her in order to solve some puzzles. Then fans can make up their minds about this. As of yet we still don't know much about her. Five episodes may be too much to ask for though, I don't see her being as successful as Guybrush, who has four games behind him.
I do like the idea of intertwining story lines. Hercules-Xena/Buffy-Angel style. Where Morgan is always one step behind Guybrush and always just misses him. And maybe runs into characters that Guybrush has wronged. But this would only be for in-jokes or to connect story lines between the Monkey Island games.
If you are going to give Morgan her own game, give her her own adventures to build her reputation with, in an attempt to keep up with Guybrush. Like how Morgan became a feared pirate hunter, how she uses the sword so well, etc. Do not necessarily show events from Monkey Island games, but hint at or lead up to, and the Player will tie it together themselves. For instance the grappling hook that will become Guybrush's hook hand, can be seen.
The prequel is a nice idea, but lets keep other options open in the meantime and maybe telltale will like these ideas.