Here’s a link to an Oct. 23, 2012 interview with Dev Team member Jean-Paul Jarreau.
Enjoy.
That’s quite an interesting read. Especially the thing about expanding the existing levels.
We need even more BM dev team interviews 
Does anyone recognize this?
Stalkyard 
That was my (second) favorite map back when I only had the PS2 version!
Right - it looks like Stalkyard.
“There’s still a significant portion of Black Mesa yet to be completed. Will it be purely new material when the remainder is released, or are you revisiting and/or expanding existing material?”
When the interviewer refers to a ‘significant portion of BM yet to be completed’, I interpret that as a reference to Xen. The question itself is a little odd. Does he mean to ask if the level design of Xen will be conceptually different from the original, as opposed to retaining the original conception and expanding on it? Or is he asking if, in addition to Xen, the levels to Lambda Core will be reworked and/or expanded?
The screenshot answers the first interpretation in terms of DM, but I wouldn’t read anything into that in terms of Xen or expanding the already released levels of BM. His answer doesn’t speak to Xen or revisiting/expanding the existing levels.
I think the question was indeed whether or not they would change or expand parts of the released product. Which I guess isn’t the case if his answer was a DM screenshot.