I don't think it's really an indicator of popularity or not since there are some big properties out there with pachinko/pachislot [pachinko+slots] machines. Not necessarily individual J-Pop stars though, haha. I mean if you look at Ayu's career right now, does it really look like she's lost her popularity?
I suppose pachinko doesn't exactly have a good connotation to it though... (probably due to the smoky atmosphere of parlors and the possibly-run-by-yakuza cash out shops)
See this
Akina Nakamori article about her second "wave" of pachinko machines. Comments are a bit harsh.
Trailer for Akina Nakamori's pachinko machine:
I imagine Ayu's will have a few Ayupan? And wow,
TRF has one too! But they've kinda... not had much luck in the later half of the last decade.