You have faith, I'll give you that but from what I've seen I can't cosign it. How good is the writing in the Halo games? How big is the story in the Halo games? I played Halo 2 for an hour so I don't know. However I do know good writing takes time especially when you're using the same people over and over again. Sometimes having a plan isn't enough. Take "A Song of Ice and Fire" for instance. GRRM has said he's known the ending a long time ago but he's still writing the books. Hell, I'll be surprised if he's finished before 2020 and he's a godlike author.
Halo 2 is the worst game out of the numbered series in terms of storytelling, so you are already off to a rough start lol. The new lead writer for the next Mass Effect only wrote Halo 4, which, in my opinion, has the best story out of all of the Halo games. It ties heavily into the lore of the Halo universe and substantially builds on MC and Cortana's characters. I can see why BioWare would want to include the guy as he shows a talent for character depth, drama, and he helmed the way for a new Halo trilogy. I believe seeking him for the next Mass Effect was very deliberate.
GRRM is easily distracted and he writes his novels on a PC built in the 80s. I'd hardly use him as an example of why a trilogy isn't a good idea. Not to mention, GoT is vary more than just three books, which is the problem. He has a lot to say and so many characters that of course it's incredibly taxing. A BioWare game will never have more than one main protagonist more than likely, so that's hardly a concern.
OK, so what would the solution in ME1 be if you knew in ME3 you wanted Anderson on Earth and the Rachni turned into reaper husks? Probably not to offer the choice. I want to see big choices with vastly differing consequences much more than I want to see a lot of cosmetic consequences to irrelevant decisions.
The big benefit of planning out the entire story, or at least key concepts along with the ending, is so they can drop hints and refer to it along the way. It helps reduce plot holes and makes the story seem more authentic. It doesn't magically reduce the amount of work they need to do to handle branching narratives.
I believe that's an assumption on your part. More than likely, those choices would have turned out very differently had BioWare executed properly. Choice doesn't need to be taken away necessarily. In fact, at least with Udina, they give an explanation for why he is now the human councilor. That would have been probably better to have included via Mass Effect 2 in the story. In all actuality, Shepard was a Spectre, so he really didn't have any authority with who was on the Council anyways other than his initial recommendation in ME1. Again, that whole scenario could have been avoided through planning.
I don't believe anybody is claiming planning ahead makes crafting a trilogy easier. What it does do is make developers stay on point and lead to a more cohesive experience. Doing a trilogy the right way will always be a challenge. The same can be said for doing a cohesive story in just one game. I've played very few games that truly did a phenomenal job of telling a story in just one game. The most memorable games I've played generally have stories continued in subsequent games.
MENext needs to be a stand alone. Written with a good beginning and a "really" good ending. All big choices wrapped up within the game. The goal should be to regain the faith of the fan base and move the ip forward. If all goes well, a trilogy could be considered for future games. Imho.
BioWare doesn't need to "regain the faith of the fan base." Most players still love Mass Effect regardless of the controversial ending to the trilogy. The only people who cry "doom" and "gloom" are those who are stuck in the past and believe BioWare committed a mortal sin beyond redemption. If anything, I'd argue the controversial ending was likely a benefit due to how much exposure and coverage it received by the media.