but should Devuan's future be compromised by Debian's foolishness, I need an escape plan.
When confronted with Linux, Devuan would definitely be my choice, but what you stated sounds like a good plan. I know many people say (quite correctly) that the BSD projects have much less man power than Linux. However this small number is still considerably larger than an individual distro that will have to fight systemd almost entirely alone.
I also wonder if developers will provide more care to port to FreeBSD as an entire operating system compared to what they see as a niche individual distro with an unknown init system. Time will tell. That said, I think the entire Linux community reverting back to Devuan is a potential outcome too (in which case we would be at the "forefront of OSS technology" again as a bonus ).