It seems that the standalone npm package hasn't been retired, which creates a bit of a problem...
As things stand in F24 we have npm providing 0:3.5.4-5 and also nodejs providing npm 1:2.15.5 and obsoleting npm < 0:3.5.4-6.
I'm not sure what happens if you update with dnf system-upgrade but if you have both nodejs and npm installed and try and distro-sync to F24 then you will fail with:
Error: package nodejs-1:4.4.5-1.fc24.x86_64 obsoletes npm < 3.5.4-6 provided by npm-3.5.4-5.fc24.noarch
Because it tries to update both packages but the updated npm conflicts with the obsolete in nodejs.
The workaround is to remove npm before upgrading, but we should retire npm I think at least in rawhide - not sure if we can still do that in F24 or if it is too late?
We should probably also find out what happens when using the official upgrade method...
Tom