I don't see any real point in including zero rating under net neutrality, for several reasons.
1. The usual argument is that if an ISP can zero rate service X, that makes it harder for competitors of X to compete, and so we need to ban zero rating to encourage competition.
This argument fails because a last mile ISP like Comcast can easily side step any internet neutrality rules in offering X by making a deal with the X provider to serve the service from Comcast's own servers. Then it is not being provided over internet and so is out of scope for net neutrality.
They could even go farther, and not even use IP at all to deliver it from Comcast to the home. They run IP on top of lower level protocols, and they could use one of those lower level protocols to deliver to an app running on the set top box, which could then serve on the LAN using normal IP protocols (which would be out of scope for net neutrality because they are just running on a LAN in this case).
If we want to stop this for competition reasons, we'll need to use antitrust, not net neutrality. Antitrust cannot be evaded by simply changing the protocols.
2. We accept zero rating in every other or nearly every other common carrier service. In telecommunications. for example, I've never seen any objections to zero rated telephone service, whether paid for by the phone company (such as free calls to government offices), or paid for by the company called (commercial toll free numbers). In transportation, we don't get our feathers ruffled when a bus or cab company offers free rides (possibly paid for by a sponsor). What is different about internet?
Generalizing this, in general we allow nearly every provider of goods and services to give you MORE than you have paid for. As long as they deliver the service that you paid for, if they want to give you a gift of more service to promote a particular offering of their own, or to promote (possibly for pay) some sponsor, we allow it. Regulation is concerned with making sure they don't under deliver, not preventing over delivery.
It is hard to make a case to the typical consumer that there is something fundamentally different between, say, Safeway giving a discount on Pepsi, and an ISP giving a discount on bandwidth used for Spotify.
3. Suppose I'm a company selling something that uses a lot of bandwidth, such as a game that requires a large download. I'd like to pay major ISPs to zero rate it. If I cannot directly do that, but the ISP sells prepaid bandwidth cards that you use by entering a code from the card, I could simply buy prepaid bandwidth this way, and when someone buys my game I could give them a bandwidth code for their ISP to cover the costs of the download. Are we going to ban prepaid bandwidth to stop this?
If we want to get net neutrality back, and have it STAY back instead of just flipping every time we change which party is in control we need to keep it to just involving things ON the network. That's basically throttling, blocking, and paid prioritization. Billing is OFF the network. I think it should be reasonably possible to get bipartisan support for those.