It is possible for Bitcoin Core to reject the HF recommendation.
This hard-fork is ... will only be adopted with broad support across the entire Bitcoin community
So, I read this as saying that nothing is set in stone yet, i.e. a HF is not guaranteed to happen.
Exactly. This is what I've been trying to tell a few people but they are unable to comprehend it apparently. There is no guarantee that the HF is going to be accepted/going to happen. Also anybody can write their own BIP (proposal) for a HF. With this agreement the developers who signed it have to make a proposal and code it before July (if they fail to do so, then the agreement is done and they lose trust && reputation).