Just to keep you up to date on the topic:
https://www.auto-motor-und-sport.de/...zoll-schmaler/
So talk is now to remain on 18'', but slightly lower profile and narrower.
Current:
Front: 305/720/18, rear: 405/720/18
Suggested: 275/705/18, rear: 375/710/18
With the introduction of the 405mm wide rears the width to height ratio was: 405/670= 60%
With the move to 18'' it became: 405/720=56%
Now with the narrower 18'' you'll end up with: 375/710=53%
That's not really a wide looking tire any more. Pirelli are so hung up on the side look of their beloved 18'', that they forget they will look pretty narrow from the rear (and like wagon wheels on the smaller 2026 cars).
For reference the initial hybrid era 13'' rears were 325mm wide and 660mm tall giving a width to diameter ratio of 49%. So this means with a 53% ratio, the now proposed 18'' rears will almost be as narrow looking as those narrow 13'' everyone hated so much.
Personally, I wished Bridgestone had won the bid. Then it would've been much more likely that we had tire and wheel sizes that made technical sense.