The consensus is behind Segwit2X which IS a UASF. The original UASF proposal is BIP-148 and Segwit2X uses a different mechanism (BIP-9 and 91? I think) but those differences are implementation details that Bitcoin.org doesn't the a problem with.
The Segwit2X and Core factions agree on Segwit. Core doesn't like later doing a 2MB hard fork, but most of us think it's a reasonable compromise. There won't be a lot of complaining.
The real threat is Bitmain which wants to do its own hard fork, that will NOT be compatible with Segwit, which they intend to mine privately and which will have unlimited block size:
That said- this is a legit notice and is probably good advice. This is a contentious upgrade.