It was posted on the XCOR thread.
Looking at reusable Delta IV 1 stage, maybe a 2 x 50klb fitted to existing stage would give them ability to land it. Not sure if they would fit. At present these a only paper engines based on article.
Not to take this too much further here, as I accidentally posted it in the "wrong tread"
I would recommend going to the linked XCOR thread if you want to see the development status. From there you will see this is much more than a paper engine. While not integrated yet... XCOR is putting all the individual pieces together. This article was about them getting a pump to work, they have built and fired a a chamber with methane that might be directly applicable, and they have run smaller hydrogen firings to get systems integration experience (i.e. ignition).
This an upper stage engine development (jointly funded by ULA and XCOR) with the focus to replace the RL10. There is no current work or concept to add reusability of either of the ULA first stages. The cost savings could be significant and the development would be strait forward with this as simply a new upper stage engine (engines being a large potion of ULA costs). Reusability is a much difficult development (costly) activity and has a questionable return on investment... And as such isn't a near term focus.
A new engine designed from beginning to use modern manufacturing techniques (eg 3D printing ,CNC) should be a lot cheaper to build.
