@G-Mon:
IMHO only the boredom is a problem here. I mean, you can build the downtown and simply not use it yet. That might save you from having to design it later.
But the boredom, ah, that's an issue which needs to be addressed. It kills neighbourhoods more quickly than any plague!

@grammapat:
Yes, the idea is that aliens are townies (although having extra human townies is ok) and playables are human. I have uploaded a townie pool replacement with 8 aliens, in case you want to use them.
Although it's ok if you want to play it all the other way round, I see that could be easier for some people... and you might consider it is humans "visiting" an alien planet, why not?

To be honest, I'm all about CUSTOMIZING the challenge. I don't think I could play any challenge out there without twisting the rules to fit my playstyle so I assume you may need to twist these. Feel free to go ahead!

There are also facial features, aliens in the game that came from alien abductions have EXTREME facial differences. My toddler's face was basically SINKING it's cheeks into itself when it turned into a toddler, they have big heads, sunken face, etc. in this game!

Yep, default pollination technician has quite extreme features and it makes for really unique children - which you may love or hate.
While I like uniqueness, I don't like it to be too extreme. Because sometimes it looks exagerately unnatural, almost cubist. So I've replaced the default PT long ago.
Also for this challenge I'm used other aliens I created - which have more pleasant features, some of them are even somewhat handsome by human standards.

I'm loosely playing this challenge. I apparently put your alien townie folder in the wrong place for Ultimate Collection because alien townies are not showing up ( I didn't put it in downloads, but in the program files, but apparently in the wrong place in the program files.)

I'm not getting alien townies, so I created CAS Aliens by using custom alien skin and eyes that have chemistry with the 5 humans I originally moved into the barracks and moved a few of the aliens into the barracks.

I moved the first couple into an apartment (1 male human and 1 female CAS alien) and she is currently pregnant. They are both family Sims that want to marry off 6 children, and I plan to try to fill their LTW. The apartment is too small for 6 kids, but hopefully they have enough money to move into a house before it gets to that point.

Lovely challenge, @Amura - I am going to try this some time.

@Orilon:
In order for a townie replacement to work, it must be placed instead of the original Pleasantview folder (N001) in the Program Files.
If you did not see any N001 folder there, then it's definetely not the right place.

@Justpetro:
Glad you like it.
I love genetics and alien so now I'm wondering why it took me so long to create a mostly-alien hood :D