The rebel ending seems unlikely to be used in G5 imo, as it makes the drakons and shapers too much alike. There wouldn't be a moral dilemma of who to help. Both sides want pretty much the same thing, using pretty much the same means.
Therefore, a third faction would have to be introduced to offer another choice, but that seems a little too avernum'ish.
Perhaps split factions among the drakons are what we will see, the new generation on one side (universal bad guys) and the older more humane ones on the rebel side. This would also give the rebels the power they need to stand a chance against the shapers - something they would be lacking if the drakons split from them completely.
I think the idea of the shapers trying to retake the Ashen islands in G5 makes the most sence.
The story could go something like this;
The drakons on the Ashen islands decide to start up a program to redevelop a new ultimate version of the unbound ones. A few of the older drakons see this, and foreseeing the consequences this would have, flee to warn the rebels and the shapers of what’s going on. The shapers immediately launch an assault on Ashen islands, but they are at a severe disadvantage since they don’t have any outposts there, and no idea of where the drakons are hiding, or what they are doing. The shapers ask the rebels for a temporary truce since they need help, and the rebels who are too weak to oppose the drakons on their own, accepts.
While the rebels and the shapers share a common goal, they have very different ways of doing things, and this will lead to conflicts. Add to that the usual plotting against each other behind the scene, and I think it’s a fairly good basis for what G5 could be.