For what purpose, though? Also, BSD, Illumos and Solaris already each are popular for certain niches...
I never tried Haiku OS, but it might be nice for people who want a free, out-of-the-box OS. I don't think it will ever be vastly popular, though, given it's technical motivation and so many literally more mature alternatives trying to fill the same spot.
I voted for BSD, because I'd love to get FreeBSD with current drivers and at least Linux-like support on Desktop. I love the Ports system and how FreeBSD is a whole system, not just a Kernel. BSDs are already popular on servers (see Netflix, who use it on most of their infrastructure) and desktop systems (Darwin BSD, which most people know as "macOS"...). It's also the reason I use Gentoo Linux, which was inspired by FreeBSD.
Illumos is the OSS Unix Kernel, and many Unix distributions base on it. It delivers a strong, vanilla ZFS, and for example, I know that OmniOS + Napp-It is one of the few small professional solutions for NAS storage on ZFS. The alternative would be slightly outdated BSD code, or the Linux ZFS port, which is also lacking behind. It's so bad that FreeBSD is now porting the Linux ZFS implementation just to get slightly better support and effort....
Solaris is the enterprise Unix by Oracle, and that's where you'd find it. As far as I know, corporations using Unix usually either go for AIX or Solaris, depending on the better contracts and available knowledge. I never used it, and I don't think it will become popular among consumers. That's not the focus, and that's ok.
The system I am waiting for, though, is RedoxOS. It's the consumer OS written entirely in Rust. The fact that it's written in Rust is one reason, however they revisit OS development and do quite a few things differently than current big systems. I'd love to see how their concepts, which seem to create quite a sturdy system, turn out. 😉