Although this is doable. It would be a fairly large undertaking. Any services and custom services currently used, would need a sysvinit equivalent. Then there is the question, would this also need to be integrated into armbian-config? Probably, yes. Would all features in armbian-config even be supported in Devuan? I seriously doubt it. Also depending on how debs specific to Armbian are currently put together and the depends they may or may not have, those would also need to be modified.
Plus it would need to be extensively tested. I have found some scripts I run that are linked to services sometimes need modification when using them on Devuan.
For a lot of boards though, on a basic level. It could be done.