The benefit of keeping the same chassis is more space for more batteries, compared to the 2018 MacBook Pro. 512GB SSD and 16 GB Ram definitely viable, but it could potentially cost more than 2k.
I'm not so sure if there will be any major redesign introduced for the MacBook. The Air could be getting some design elements that already exist on other new MacBook models, and that isn't really worth an event. Usually, events aren't held for the unveiling of processor/ incremental updates either. I think the Air will not be significantly reworked because it's suppose to be a "budget" laptop, and the MacBook's design hasn't reached the end of the cycle. My guess is that the non-touch bar Pro will be ditched in favour of the Air, and to further differentiate the Pro from other MacBook models.
Unless another Mac-related product is receiving a substantial refresh (e.g. Mac Mini) or some surprise product is coming, I think an October Event will likely not happen. But I wouldn't rule anything out...time will tell.
i certainly think that there will be a build to order configuration, they do this on every Mac from the MacBook Air (still) up to the iMac and iMac Pro. If they want to bring higher specs (not as high as the MacBook Pro tho) then 16GB Ram could be an option along with 512GB os SSD storage.
I don't think they will redesign the MacBook, it's been 3 years since it was introduced and Apple typically wait longer for design refresh's, they will probably give it a spec bump tho. I can see them talking more about this updated Air, don't forget the Air is 10 years old this year and Apple like to talk anniversary's when they have a product ready. I don't think this new Air will be massively redesigned, people love the current design i think there will be tweak tho with the bezels getting reduced (as Mark Gurman reports will happen).
I think at this point it will be a MacBook Air, Mark Gurman called it the Air by name in the latest report which is something he didn't do before. I agree tho i think the none touch bar will be removed in favour of this new Air, i think it was Phil Schiller or Craig who said initially that the none touch bar was great for the Air users, now that they have this new Air in the works it's pointless, i think that's why they didn't update it when the touch bar models got updated last month.
I think the following will be the lineup:
Macbook Air - starting at £999 (with a build to order config that will go higher in price)
Macbook 12" - spec updated with latest Core M processors, maybe given True Tone display and 3rd gen butterfly
Macbook Pro - was updated earlier this year with much faster specs, True Tone display and 3rd gen butterfly
The removal of the none touch bar MacBook Pro leaving only touch bar MacBook Pro for both 13" and 15" versions.
I went back and rewatched the old 2008 introduction of the MacBook Air and Steve jobs put up a slide that showed the same lineup (MacBook, MacBook Pro and MacBook Air) i think it makes perfect sense to go back to that, lets not forget that they removed the white MacBook at one point and then brought it back in 2015 with a redesign which brought it more up to date, could that be what they are doing with the Air? the only difference being that they have kept the old one around because it still sells well.