No, I don’t see any side effect. However, as @uliversal said in a previous post, recent guidelines from Microsoft prefer a third level DNS domain (i.e. ad.nethserver.org) over a non-existing TLD suffix (i.e. nethserver.local).
Today the choice of the machine FQDN is bound to the Active Directory realm name. If we split them and implement a Realm parameter it would be easy to configure a mail server. The machine FQDN is free from AD requirements and vice versa. Accounts names with @domain suffix can correspond to public email addresses by default.
It could be possible. We want to fill any possible gap with ns6 features. Changing the FQDN is one of them.
As usual this is a gradual process: NethServer is a rolling-release distro and we just entered the v7 stable branch. I think the best is yet to come 