How do you feel about the premise not happening due to the Reaper invasion?

I actually don't think that one is a retcon. Aethyta in ME2 mentioned proposing to the Asari Matriarchs that they should focus on making their own Mass Relays, though was laughed at for it which is why she left Thessia seeing her leaders as worthless. Maybe some other people considered the idea and decided to move on it. We do know how Mass Relays work, at least to an extent, since that was information left for us by the Reapers for their cycle to work. We also know that it is possible for a cycle to do so, as we see with the Prothean's Conduit Project. Speaking of, AI would have a couple years to play around with it, and it may be where we get the technology for the stasis pods as well. 

As for profit, yeah actually. It would cost an unimaginable amount and I have issues with them spending that much in a decade, but the return of investment is literally an entire galaxy even bigger than our own. 

1) Citation needed. It is never said why Aethyta was laughed at by the other Matriarchs. It could have been for any number of reasons. And Ilos is never said to be restricted by the Council, and instead that there are Salarian researchers there. The only race or group said to be restricted from Ilos is the Batarian Hegemony. Ilos is open enough that painters were even allowed, as shown by Liara having a painting of Ilos in her apartment. 

2) Now you are arguing capability, not motive. The tech is still an issue I have as I have expressed many times but it isn't relevant to the thing being discussed. 

False.

The risks cannot be compared. The investment needed to the trips of the 15th and 16th centuries were small compared to the amount the Arks would need. We are talking a kind of money that the codex said shouldn't be possible in the first place. 

The profit? Unless Andromeda has something the Milk Way does not, and that would be some kind of alien technology, then it would be null. Why would one go to Andromeda to get something you can get anywhere in the Milk Way? So there would be no profit involved, it would be like traveling to China or India to get grapes or wheat. Not to mention the time involved, the trips to India gave huge amount of profit in a few years, while the AI would maybe give nothing after centuries. 

The only similarities are in very superficial level. 

He also managed to get Ogre statue, so I wouldn't underestimate the guy.

If you say so.

Yeah, I'm serious kemosabe.

Serious as a Mass Relay to the knee - oh snap, the technology does exist.....it's just Reaper tech so therefore no one remember's it's a thing.....

and 2185, the year this voyage launched, was also the year someone FINALLY took a close enough look at the relays to go "Huh, these are way older than the Protheans"

You really think anyone has examined them close enough to actually BUILD a pair?  Because, there would already have to be a relay in the Milky Way for this crew to build a twin in Andromeda to actually get a path working.

I'm starting wonder why the Asari, who had interstellar space travel capabilities centuries before the humans, never undertook a voyage to Andromeda themselves if it's just 600 years (around 75% of a lifespan) to them. They could've done a two-generation voyage.

Perhaps the 600-year-travel-time was made only possible with the discovery of new Prothean or reaper tech after Mass Effect 1.

Except the civilization that built the relays was the Reapers.  Or, possibly, the Leviathans and the Reapers re-purposed them with the Citadel.  Either way, neither of them are at all interested in younger races rising above their station.

Somewhat more probable would be an artifact from Andromeda making its way to the MW, (like the other Clarke novel, Rendezvous With Rama) and soldiers, researchers, etc hitched a ride on it.

Well, they're a fan of that, since ME2 at least.
I'd say humanity's rise to power before ME was conveniently too quick, but it was more backstory then the plot of the game.

They wouldn't need to be able to make Relays. I would have thought they could just take one with them.

Well I actually hope it's nothing like that... It may be some kind of VI or just some kind of platform to open something else.