The limiting factor is hardware availability.  If you can supply hardware for testing, we'll be happy to try. 

so far as I can see, it'd probably be a good idea when different ports get underway to put up a page full of the different hardware that would need to be donated to the cause to get these rolling. Once that happens, there's a good chance that others and myself at the very least can then point that page at people and say "hey, you guys got anything they need?" and then the magic of the internet itself takes form... possibly. if anyone's on good speaking terms with any of the Debian maintainers of the various ports, it'd possibly be a good idea to ask them about their test hardware to get a good idea.

I can at least say for PPC/SPARC, anything that solidifies support for either at this point in time is going to be big news on various Linux-oriented news sites and such. some other distro other than the "norm" may just bring back those that are about to switch to a *BSD or retire their machine; more-so for PPC/64 than SPARC64 since that's back in the game for Debian and neither have left Gentoo support so far as I know... and the best part is, no systemd!

Mainly, I'm interested in seeing two architectures getting worked on aside from the current:
-PPC/PPC64, due to the drop of such from Debian after 8.x; this leaves out all Apple PowerPC oldworld/newworld 32-bit systems and their 64-bit counterparts in the G5 range from Stretch. the current roadmap for Debian points only to everything Power7 and beyond.
-SPARC64, which WAS dropped from Debian Jessie and brought back with Stretch after interest grew back in that port.

I've been following along with Devuan as the better part of the last year has progressed, and it has been hinted that quite a couple of Devuan developers did have access to Sun hardware for testing SPARC64 on bare metal, when I did ask about it in the IRC channel. I'm not sure about PPC Macs. At the current moment, there are at least more than four machines to my knowledge between a friend and myself, that still use Wheezy-sparc64 in what can be considered 'production' with some hardening in effect for security purposes to keep them safe and running without issue as time goes on; There are also at least two ppc64 systems also on Wheezy. Neither he nor I have any real desire to upgrade to Debian Stretch-sparc64 or Jessie-ppc64 in the future due to heavy systemd integrations, and we are considering moving away to Gentoo or OpenBSD for these machines, as there isn't a clear proper debian-based nor debian-forked successor at the moment.