Committing genocide against the Kett is a must?

Sure, why not.

If it is a necessary evil depending on future context.

Sweet Jesus, BSN.

I don't think Jesus wants to peek in here.

Hopefully not.

One of the issues with allowing the player to determine the fates of entire species or factions, is that makes proper sequels difficult to do. How do you create a sequel in that setting when an entire species might be extinct in some imports, and alive and well in others?

Allowing the player character kill off the Khet would probably mean they'd have to set the next in game in another galaxy, and continually moving to new galaxies to avoid having to deal with choice & consequences in the last, would quickly get old.

The impact of player choice should be more small scale and primarily affect your inner circle, so that it doesn't completely bork the setting. Any impact on factions should be limited, like the decision of who to crown king of Orzammar in DA:O. That choice has Orzammar taking diverging paths, but it doesn't result in a situation where the city-state is overrun by darkspawn in one import, and still standing in another.

As a wise man once said:

"...With the terrorists, you have to take out their families..."

Only if before nuking their homeworld from orbit while wearing sunglasses you get to ironically paraphrase Oppenheimer the creator of the first A-bomb who famously proclaimed  "now i have become death... the destroyer of worlds" (bhagavad gita reference) essentially proving he was correct in his assertion.

By 2016 BioWare and under Mac Walters? Not happening...

Well, there is a disturbing theory about how evil the opposition are...

We all know damn well Bioware won't go there. They are interested in telling their story and we get to roleplay within the confines of that. They want to paint humanity as the morally superior species, and that's hard to do if if you're slaughtering entire species. Besides Bioware just isn't good at handling "morally grey" or highly controversial material. They're very risk averse. Besides they've already stated we're in Andromeda as explorers, not conquerors. And really it would be hard to conquer a hundred solar system area of a galaxy with a few hundred thousand members of the various races unless the races we encounter are technologically challenged. So no, sorry, you won't be seeing any subjugation/annihilation of species in MEA.

While true, all of those were mistakes. It's partly why this game is set in Andromeda and not the Milky Way.

The only way you could have a Milky Way sequel at this point is either to ignore completely any previous choice that implies a faction could disappear entirely (having the Geth present regardless of ending choice for instance, and hand-waving it as the Geth as having been rebuilt after ME3), or to not include any faction that could be destroyed in the previous game. In the latter route, you'd get neither Quarians or Geth in a Milky Way sequel , and the only mention of either would be in the codex.

If the Andromeda writers are smart, they won't write themselves into similar corners.