I remember watching this clip years ago. I believe it was part of the DS DVDs extras at some point. When I watched it I thought it was great that even JB believed Elizabeth to have been Victoria's mother. Although her word doesn't necessarily confirm it as cannon, I think it's a widely held belief within the fandom that this is the truth.
If only that plotline hadn't been dropped during the early run of the show, it could have provided a great opportunity to explain the origins of Vicki during a flashback, similar to 1897, but maybe only going back 20-30 years to show Elizabeth as a young woman.
Also, for those who have read "Heiress of Collinwood" by Lara Parker, you may remember that this was addressed. I was highly disappointed in Ms. Parker's take on the story, especially because it seemed to stretch the truth and the timelines quite far in order to somehow make this all work.