They’ve stated this multiple times from project conception in interviews as well.
From the verbiage of the first paragraph it seems “[Blizzard] is not going to raise that cap any further.” That said, I’m not sure what “further” relates to due to ambiguity; it seems they are referring to the 2006 vanilla cap being raised further, but I’m not sure if there was information about it being risen before this post - thereby, we’ve raised it somewhat over vanilla but will raise it no further.
It seems to me they mean the servers have a vanilla cap.
Just playing on any of the servers and it is brutally apparent this seems inaccurate; I played on full servers in vanilla and outside of peak days/events it did not feel this consistently full to me.
Nevertheless, it seems further information from Blizzard on this would be welcome since I’ve seen conflicting info all over.