I thought that, but then patent drawings can also be quite vague beyond the pure numbers (and the specifics of the patent) - I think while it's likely Mazda has the basic geometries etc of the new car decided (such that they can put them in a patent doc), I don't think the drawings in that parent are necessarily accurate to the real car other than the position of certain things. It is after all primarily about the doors. For that reason I'd also assume it's probably not depicting alloy box sections, more just very simplified outlines of where certain chassis components will be.
For a Miata at least. The MX-5 is too high volume and its price point needs to be relatively accessible, and I don't think aluminium would be viable at that scale (sadly, give how much they like to rust).
For a lower-volume (more expensive) sports car based on the Iconic SP though? It's a possibility - Alpine showed it's possible with the A110. That was a £50k car (around $70k) in the UK, so I'd assume that's probably a minimum viable price for an all-alloy sports car.
The 1.5 was a much nicer engine than the ND1's 2-litre, but from the ND2 onwards I think the 2-litre feels just as good, and as the 2-litres are usually higher specified than the 1.5s (firmer suspension, more bracing, LSD etc) it's very difficult to tell if the 1.5 feels lighter, even if the scales suggest it is. I've never driven them back to back but the 1.5 and 2.0 feel very similar to me, other than needing to rev the 1.5 a lot more to get anywhere.