Quarians Held Up By Roekaar

If the geth were the problem, why would the quarians tell them to stay away? The geth are more or less a known quantity. Now, if it were something stranger and more terrifying, then I could understand the warning. Geth being the problem just doesn't hold up for me.

Even in ME1 the only Geth that were outright malicious were those aligned with Sovereign.  Sure their were others that were hostile if you got in their way when getting the geth data for Tali, but those were the only Geth we saw in ME1 not aligned with the Reapers.  If the Geth stowed away on the Quarian Ark there isn't any reason they would try to subdue the sleepers or take over.  This could also perhaps be another faction of Geth that reached a different consensus in favor of working with Organics, basically the opposite of the Heretics.

I imagine once the Quarians started waking up and found Geth aboard it all turned into a huge misunderstanding, some small scale fighting and the Geth being locked in a portion of the Ark till Ryder shows up and solves the situation.

Basically all just a big excuse to bring the Geth to Andromeda.

Not the Roekaar but who is to say they aren't fighting a Angara. The Angara were artificially created by the Jardaan. What if not all Angara live in Heleus and have evolved to be welcoming

The thing that intrigues me about the Quarian ark is - why would they not ask for help? In fact, the Quarian Pathfinder specifically warned the other species to NOT come and help. If the problem was the Geth or the Roekaar or the Kett, why would they not ask the other species to come help them?

The only thing that makes sense is if their problem is contagious (virus?) or any help will also doom the helpers (a trap). I suppose they could be stuck in the Scourge and don't want others to come because they would get stuck also? These are possible but still don't make much sense. If the problem is contagious, they could just warn the rescuers so that the rescuers don't come in contact. If it's a trap or the Scourge, they can warn the rescuers about the trap or the Scourge.

I hope Bioware has a cool story to make sense of the Quarian ark - but I expect they'll come up with a reason that don't make any sense. Expect the worst and hope to be surprised, right?

The Tempest uses the same sort of drive as the arks (IIRC), and they can obviously travel further than Heleus. It's just rather slower than using mass relays. If it involves a few weeks or even months Ryder could get there.

I share your view about the Reapers. However Andromeda seems keen to put that behind ME (what mentions we got were probably the minimum necessary to account for them not being able to be in contact with the Milky Way).

Geth are software.

They could infect nearby ships and take control of your airlocks.

Staying away from would trap them on the ship because they dont have physical bodies to inhabit they would be able to fly the shuttles and fighter ships though.

It wouldn't be wise to approach them.

I hope the Geth aren't the threat and if involved turn out to be allies. Now I can see them doing it where Ryder and Co think the Geth are involved since they think all Geth are like the Heretics but sometime in the DLC we encounter the Geth are learn they aren't the enemy and help us defeat the real enemy.

I also don't think the Geth should be stowaways on the quarian Ark. It'd be better if they built their own ship that came to Andromeda and they too got the signal and followed it thus getting involved.

For the actual enemy, I think a new race would be interesting. Bioware has a pattern of introducing a new race in the DLC cycle of each game(ME1=Batarians, ME2=Yahg, ME3=Leviathans) so it would fit the pattern. 

Yes, the Geth used three Mass Relays to make a FTL telescope that gave a relative real-time look at Andromeda, including the Heleus Cluster. I don't think it is specifically mentioned what the Geth were looking at, but there are a few guesses. 
The Initiative got that data because some quarians managed to get that data and gave it to the Initiative. 

Yeah, if we are capable of building ships capable of reaching Andromeda the Geth certainly are able to. They are more advanced than us and they don't have to worry about organic concerns for the voyage.
Plus they wouldn't stow away because "Geth do not infiltrate".

Why would Reaper follow an Ark for 600 years without blowing it up the moment it came into range?

This us almost as bad as the Vetra is Sarens daughter theory.

Interesting idea... though just somehow a bit... implausible.

honestly given the way its worded i dont think its anything Kett or Rokkar related. It sounds more like they've put them selves in a quarantine to prevent something getting loose. what that something is though i couldn't guess.

and wasnt that fun trying to word with out spoilers but yeah thats my take on it.