It turns out that the interview in question was actually conducted back in 2015, which sad to say makes these quotes largely redundant. Apologies for getting your hopes up.
The Witcher 3: Wild Hunt became a runaway success for CD Projekt Red back in 2015, and the studio has on several occasions said that it was supposed to be the final game in the series. Perhaps it doesn't have to be that way after all though, according to CEO Adam Kicinski. He was interviewed on Polish TV and said it wouldn't be fair on fans not to make a fourth game:
"It would be unfair to fans not to make one. We have been working in this universe for more than a decade now and I do not think it's going to be the end of it. It is still early to talk about it, but we have not forgotten this series."
Next up for CD Projekt Red is Cyberpunk 2077, which is supposed to be released next year or more likely 2019, but the developer has grown immensely during the last few years and they might have more than one big team these days. Judging from what Kicinski says, it wouldn't be to far-fetched to believe that a smaller group has started throwing around ideas relating to The Witcher 4.
Thanks, Segment Next.