Yeah, they chop and change(their minds) all the time there at Nikon HQ.
Can't recall exactly but the D7100 was always touted as a D300(s) type replacement, where Nikon had a long long break between the D300/D300s twins and then the subsequent D500(ie, no D400 in there).
So maybe that was the overall model iteration idea, but then changed or whatever.
And then they did something similar to the D800 -> D810, where more of the D810's body went with plastics ... not all, just more than the previous model had ... and all the internet warriors went crazy.
Nikon addressed that and gave the D850 full metal jacket.

I wonder how many D810 have seriously failed with their more plasticky bodies?

Plastics have their place, and metal has it's place .. but as said before if I had a plastic or metal option for some specific thing(say a tripod) .. plastic would easily win for some things. (noting that carbon fibre is a plastic )

Plastic camera body .. never really bothered me much.
My D70s had it's fair share of use and a little abuse, same condition as my D300(ie. very good to excellent), but the D800E did fail in a metal to metal/plastic joint .. the 10 pin port gave in.
Only part that I'd say would be better made in a lightweight sturdy metal tho is always the bottom plate. That's the main area I feel you feel a difference between plastic and metal.