Tough question. I'm a bit younger and my backer # is in the mid-3000s, so in my case, I feel like it would be better to save the cash towards an 1180 or 1180Ti, which hopefully will be available by then. That way you'll have the best possible experience with the 8K. That's my plan.
If money isn't an issue, then why not? If nothing else, you'll have PiPlay installed and your VR transition to the 8K should go more smoothly. Depending on your situation, you might have a grandchild who would love to get a 4K hand-me-down.