It depends on which segment of the hobby. If you're into postwar or anything conventional, then the Golden Age is never over because of the amount of used product out there.
However, I like modern-ish diesels, scale stuff, and only midwest road names. Almost everything I own was made since 2010. I grew up in the 80's and have no memory or nostalgia for postwar Lionel. For people like me, I think the Golden Age is over (or at least on a long hiatus).
Two Lionel catalogs per year and that's it.
I'm optimistic that battery power will revolutionize things and new manufacturers will surface in years to come. Until then, it might be pretty sleepy. Just my opinion.