Udina, Cerberus and the VS

Maybe... I think that the VS was more of a meat shield for Udina, and once Mr. Lamo and crew showed up, I'm willing to bet he'd have no problems shooting the VS in the back once they dealt with Shepard and Co. (if the VS killed them, that is).

Maybe but there are tons of Spectres out there. Which doesn't mean it's not his logic.

I completely understood this. He knew for a fact that Earth was hit hardest and the asari Councilor outright side that was okay but it would buy them more time. Of course he's looking for anyone at all to help and an organization that is powerful and works on behalf of humanity is the obvious choice. There was literally no one else, which was a bad position to have been stuck in. By the time he realized it was a mistake (assuming he did), it was too late.
I didn't know this but once From Ashes became a DLC this was no longer possible.

True A/K would be sidelined for that time, but it would make sense since the way it currently happens doesn't. Nothing was gained for Cerberus. The mission backfired. That's the fault of the ponytail. The link I provided mentions a few other things that would have been different. I prefer that version vs the version that was released. It would be one of many reasons to remake ME3 or the trilogy.

Hmmm... That could work.

My understanding of Udina in ME3 is that he's pretty much just under the Illusive Man's thumb, desperately scrambling to keep the situation under control after realizing that the shadow organization he's been dealing with and can't extricate himself from is on the enemy side of an extinction war, and a single whiff of the fact will have C-Sec kicking down his office door.

IF he used his influence to force Kaiden through as a Spectre candidate then it was most likely originally at the Illusive Man's behest for some other long term plan before he was forced to improvise to try to maintain his cover during the evacuation, rather than because he had a personal animus against Shepard and was planning to orchestrate a showdown. I don't see him rocking his leaky little boat by trying to cook up some scheme against a galactic in the middle of the war effort. No matter how enormous a shitload of paperwork and headaches that hero has caused him through the years.

Personally I'd say Kaiden/Ashley advancing through a combination of merit and the Council speeding things along and lowering standards in a crisis feels plausible enough on its own.