People predicted that 2 years ago.
If they intentionally bought 8 core CPUs for gaming, well, they made the wrong investment. Not to say that the CPU is instantly rubbish, but they didn't get what they were hoping for.
2~3 years has passed with very limited games that support 4 core CPUs, what makes you think that 8 cores could be utilized decently within the next 2-3 years?
I'd stick to 4 cores if I were OP.
I don't agree that futureproof doesn't exist. But I think it only exists when you can see a trend. Currently even 4-core games aren't everywhere, I really wouldn't bet on 8-core games showing up in the near future.