The HK agreement between miners and blockstream (basically Core) represents consensus. It clearly says both 2 MB hardfork and Segwit to be delivered. Doing one but not the other one is actually stalling - not to mention breaking intentionally agreement is quick way to loose all credibility - not best day for Bitcoin if it really happens considering blockstream basically represents Core, the most used Bitcoin full node implementation today.
Blockstream does not "basically represent core". That is a common misunderstanding spread by r/btc FUDers.
Blockstream was created by several of the most active Bitcoin core developers. It represents over 10 Bitcoin core developers who provide together most commits to Bitcoin core. So blockstream basically represents Core is true from this perspective.
We will run a SegWit release in production by the time such a hard-fork is released in a version of Bitcoin Core.
So...
not running a Segwit release
before the HF version of Core is released is perfectly allowable by the agreement.
You nailed it. The agreement allows this, plus it makes much more sence for Core to merge both HF and Segwit at the same time so the HF change is not as problematic for non mining full nodes as well (who sometimes dont upgrade so often and Segwit is handy).