I appreciate that Google appears to have reached out to local newspaper sites (qctimes.com, napavalleyregister.com), for Contributor. But if I were a major content publisher, the relatively small and mostly non-notable list of current Contributor sites [0] would make me think that Google isn't highly invested in this project. Which is not a good first impression considering that many people think that Google is too quick to abandon projects. They should have booked a few more major sites and media brands; right now, the 2 sites that are highlighted are the National Post and Popular Mechanics.
IMO Contributor is still pretty new, and without users the time and effort spent implementing it probably isn't worth it yet, especially because many of those running adblockers just ignore it entirely (I can't even count the number of times I've read "why pay for contributor when adblockers are free?).
If/when it hits a critical mass of users, suddenly it will become a lot easier to justify the cost of implementation.
Hopefully tools like this can help get some sites to implement contributor or something like it so paying for access can get a foothold and become a viable option.
Funding Choices and Contributor seems to be good choice for small-to-medium blog/news site operators. Compared to Flattr and others I see the potential here to fund a news outlet entirely with this services.
[0] https://support.google.com/contributor/answer/7324995