The 607/587 debate remains relevant* because the WTS couldn't just drop that date, since it was tied to the 1914 predictions that Russell made. There is a lot that they can revise, such as the predictions themselves, which they modified to make it seem as if Russell was given direction from Jehovah, and which was a big part of the sales pitch for so long. But Russell's math needed the year 607BC to get to 1914, so they couldn't give in on that point.
I wonder, though, if that will change soon. 1914 itself is becoming an albatross for the WTS and no longer serves the purpose it once did, both as a recruiting device and as a way to keep the rank and file on tenterhooks. I suspect that they will ignore it and let it fade into irrelevance until they feel it's safe to discard it, at which point they'll gain new light about the 607/587 dates.
* Well, I mean that it remains relevant as a discussion point amongst JW supporters and critics. It serves more as a curiosity for exJWs and a defend-at-all-costs concept for JWs, at least for now.