'Evacuate Earth' Problems, Scenarios and Possibilities:

Yeah, it was both focused and flawed. That's the show they wanted to make though and we watched it. I still see it as being valuable as a thought exercise in possible doomsday planning. You have to take stock of our resources and willingness to adapt and use those resources as a race of beings for survival at the spur of the moment.
Can we save ourselves "today" if we had to? Do we have the technology, the resources, the manpower . . . the willpower to set aside our differences and individual problems to get it done? Maybe so, but there's still a lot more to explore than just what the show provided us with. How about a few more ideas.

'Selecting best genetic candidates decades before the ship is actually finished.'

Though it's still early in the mission, finding and selecting good candidates early is helpful. Since the people they choose may not actually be the ones ultimately boarding the arkship scientists in charge can screen their choosen mates for genetic compatibility and then ensure that their mating bares the children (the ones who will ultimately be boarding the ship) with the propper genetic traits they were wanting all along.
This whole thing is vulnerable to corruption though as the rich will likely begin geneticly altering, or even creating, their own offspring to be as perfect as possible. This ensures that enough of their own family makes it onboard to continue on.

'Rescuing the Rich'

The title of that was completely wrong by the way as no one actually rescued them. The rich tried to save themselves and failed.
As for the rich trying to save themselves, there's two ways it can go. It'll either happen as was shown, and very likely succeed knowing their resources, or they'll subtly worm their way into the Horizon Project and corrupt as many levels of it as their money and resources will allow to ensure their family and closest friends make it onboard.

'Religious Fanatics'

You'll get at least two extremes. One will proclaim that God has sent the neutron star to destroy the Earth and humanity because they don't believe it should exist in "their" universe anymore as we as a people are unworthy. These will be your terrorists that try to stop the project any way they can. Those landmines around the compound? Yeah, the project will definately need those to stop the crazies.
The other type will proclaim that God will ultimately save humanity and that we shouldn't try to save ourselves. Trying to save ourselves would be a sign of a lack of faith in God's power and mercy and it would be proof enough to God that we didn't believe in them. We would then not be worthy in their eyes and should then be allowed to perish.

'Rescuing the Rich Pt.2'

If the rich can't get a big enough foothold in the Horizon project or the arkship they will keep pouring money into scientific research. It would be quite possible that through their efforts a new type of propulsion would be discovered, such as an anti-gravity drive system or some hybrid propulsion design that is more fuel efficient or can potentially be renewable. If they get the drive system perfected within the first thirty of the seventy-five year time frame they would still be left with a probable good thirty more years to design, build and launch their own craft before the radiation and gravity distortions of the neutron star becomes too intense to survive.
Then you've got to wonder about everyone still involved with the arkship project. Do they continue on with their nuclearbomblet propulsion system or do they abandon it in favor of the new system developed by "the rich"? If they abandon their method can they redesign their ship to accept the new propulsion system, will they have to start from scratch on a completely new ship or will they somehow merge their resources with "the rich" in order to finish a new ship faster than either of them could on their own with "the rich" now having much more control over the ark project than was ever intended?

'Rescued BY the Rich - aka: Not Without a Fight'

Impending doom leads to desperation and desperate people can surprise you with their ingenuity. Some people just won't accept defeat in the face of seemingly certain death. You've got about forty years to come up with an alternate solution and another twenty to make it happen before things get entirely too hairy for the planet's future and humanity's survival. (my numbers are probably off on that one) The rich see a seemingly unstoppable killing machine headed right toward them and they stare up into the sky and shake their fist at it.
The rich put together a think-tank filled with the brightest minds they can find, allthewhile not forgetting the geekiest and nerdiest science fiction fans on the planet to include some off-the-wall creativity in the mix. In less than two months they have two feasible possibilities.
The thing is called a neutron star and there is no known matter or force available to stop or even slow it down. Matter can't do a thing to it, but what about antimatter, energy or both? It's a long shot but out of the two best options, an antimatter bomb or a particle beam, the rich decide to build the most powerful particle accelerator in existence and a ship to transport it out in the solar system to meet the neutron star.
With twenty years left to spare the ship gets underway and in just over three years reaches its destination just outside Jupiter's solar orbit. After testing and attaining optimal targeting alignment the accelerator revs up and begins sending a myriad of charged particles at the slowly approaching neutron star. Though it takes weeks of trying and watching the results the right beam composition is found, unfortunately the effect is minimum. The rotating neutron mass shruggs off the beam making effective damage impossible.
The decision is made to use the last of the ship's resources to get into position and aim the beam at the star's axis. Eight months later the ship is in position and begins its slow assault on the star's southern pole. With the final bit of usable matter the crew succeeds in destabilizing the star enough to alter its course sufficiently away from the inner solar system.
---
The Earth is saved but now a nearly completed arkship orbits the planet without a mission and without funding to complete it as money and resources are released back to the world for recovery efforts. Chaos, disasters and civil unrest have plagued the planet for the last twenty years and even though the planet will remain as a whole the damage and devastation have taken their toll on the people, the world economy and the environment. It's going to take centuries to recover, if the planet even can. The question arises. Do we even try to recover or do we finish the arkship and head out into the verse to find our destiny?

Thanks for reading. What are your thoughts on an extra-terestrial doomsday scenario? Tell me some things that I missed.

Ignoring "the hype" since 2008