To be clear, that isn't the final spec. AFAIK, we don't yet know the extent of changes that may be made to Argon2. The email says that Argon2 will be the "basis" for the final winner, which could have some interesting results.
I expect there will be a long review period before the winner is considered suitable for common use. It reminds me of the backlash at NIST for some late changes to the SHA-3 winner, Keccak: https://en.wikipedia.org/wiki/SHA-3#NIST_announcement_contro...
I don't expect there to be a similar community reaction. NIST and the PHC panelists (list at https://password-hashing.net/) are two very different bodies.
Argon2's internals will likely be altered (with community input); Keccak's internals were left alone (only parameters were tweaked).
The community wants modifications to Argon2 before its final publication. Essentially, each of the five supreme finalists possess nifty properties. It'd be nice if Argon2 could be modified to possibly have some of these too.
That being said, I do expect you're correct that the winner will not be in mainstream production for a couple years at least.