Please keep the focus on the original idea of the initiative and keep the Defender/Smartscreen garbage away from this great project. No one looking for maximum performance in a computer will install AV, even more, Defender, is the worst of them all.
If someone is afraid of getting viruses, I give his this advice:
Install a virtual machine with a good AV to scan everything it considers suspicious.
Use common sense when installing SW or surfing websites. This is the best AV.
If you can't resist the idea of having Windows without AV install at least a decent one like KAV, NOD or similar.
Use the original windows version without MODs or install other tweaks.
Including Dender/Smartscreen in Altas is a departure from the original spirit of the project.
If in the end you decide to include it, please at least leave the option during installation to remove all traces of that cancer.