Assuming Debian Stretch still uses non-systemd networking configuration (which was the default case in 8 at least), or Tails switches back to it, systemd shouldn't impact what Tails tries to do in any way.

Why is that important? Especially considering Tails has worked fine using systemd in their previous version based on Jessie. Additionally, Tails has used systemd's service namespacing functionality as part of a defense-in-depth strategy. Switching to Devuan makes little to no sense based on this track record.