I certainly think it's still alive, but there's less of a need for it now given how far cases have come.
There's some fantastic mod projects on these forums even, I just think that for the average person wanting a "cool looking PC/has good cooling" etc there's actually tons of stock options now, as long as you can make a tidy build you'll be grand. I remember buying a dremel kit and a few other things back in the day to alter cases but it's just not necessary anymore, that and I lack any sense of artistic flair on top outside of appreciation for what others can do.
Not so fond memories of taking the HDD cage out of a Antec 300 and adding a larger side panel fan for the GPU! It did not go as planned, but was at least functional in the end and I was happy enough with the results. Now I can spend £40-50 on a case that fits my cooling requirements with minimal fuss, let alone the higher end stuff on the market.