E.g. can they ask google.com for $1B to renew and mygrandmascookiecompany.com for $20 to renew?
So Ethos wouldn't be able to screw over existing registrants with non-uniform renewal pricing.
Source: Section 2.10(c) of https://www.icann.org/sites/default/files/tlds/org/org-agmt-...
For .com, .net, .org it has historically not been possible to price discriminate like this.
For the "new TLDs" (the explosion of new extensions we have seen in recent years), the registry contract is different and they are indeed allowed to do this. They call it "premium pricing".
Part of the big outcry about the recent changes to .org is that it brings it closer to the "new TLD" model, which disfavors the registrant.