I'm sure Tesla could spoof what the car tells you, but in my 2018 S, it tells you on the Software page what hardware version you have (mine is 2.5). I mean, you would hope they would make it say whatever it really is but you know, they can make it saw whatever they want.
To me it's about that radar that was in the leaked images of HW 4. I get that we might get nicer cameras and maybe a little bit more processing power, but to me it's all about the new radar if that somehow offsets / lessens the loss of USS. New cameras would also be nice for Sentry Mode. But for me, still can't wait to get my plaid and it will be an added bonus to get HW 4. If I had to bet money, a version 5 hardware will be out before they make it good enough FOR ME to want to use it on a regular basis.
I'm sure that for some buyers, they may look at my 2018 with v2.5 as a downside since v3 came out, but there will be buyers for it regardless. Same with the plaids with v3 vs v4. They are insanely fun and nice cars.