Wheelbase would be exactly the same.
Overall length would increase by 3″ approx excl tyres.

No it won’t. Wheelbase usually increases, but not as much as you’d expect. Chainstay lengths increase, but not by the inch and a half you’d expect, usually about half of that. Then at the front end, 29ers typically have a slightly steeper head angle to compensate, but not so steep to make the bike twitchy (which it would be if it had the same wheelbase as an equivalent 26″ bike).

Then there’s the extra overhangs… Another inch and a half at each end.

I’d expect a 29r HT of similar design/spec to be about 4-5 inches longer than an equivalent 26″, measured from end to end, so yes they are a bit more of a PITA to transport. Can get a medium sized 26″ HT or my road bike inside my 3 series touring (rear seats flat) with both wheels on no problem, but have to take the front wheel out on our 29er’s.

One of the things that’s changed is that a lot of bikes are getting longer anyway. So whereas 5 years ago packaging 29er wheels was a problem and would often lead to the bike being stretched, these days it’s more practical to just make the bike the length you want it to be, meaning packaging the wheels and suspension is simpler.

Likewise trends on chainstay length- after years of trying to make 29ers as 26ey as possible now manufacturers are more comfortable letting them be the right length.

My 29er’s pretty bloody big, it’s a medium the size of some XLs, and literally inches longer than my old medium. Not because it’s a 29er, but because it’s a beast. And if I was to go back to small wheels now i’d want it to be every bit as big.

(and back to the original question, it’s not just overall length that changes how it fits in the car- wide bars and big wheels mean it’s harder to pack it in too, since even with the wheel turned it’s still bulkier)

My first 29er had a slightly shorter wheelbase than the 26″ bike it replaced…