I'd say the redesign might see an October event as a high-end 16"+ model , $3299 starting point isn't far off - that may even be conservative if it's OLED. Otherwise, we'll see it in 2020, probably with more penetration of the line. If we see that beast in 2019, the 2020 and even 2021 models will work its new features down through the line - think Retina transition - first a high-end 15" (16"+) model, then all or most of the 15" line plus a high-end 13" model, then the remaining old models disappear..
Even a 2020 redesign will (unfortunately) very likely feature 10th Generation Rocket Lake (14nm+++++++) CPUs for the 16". I haven't seen any signs of Ice Lake going above 4-6 cores and 28 watts by then.
Apple notebook line by late 2021?
MBP - 16.4" and 14" - Intel powered (updated within a reasonable time of new CPU releases - they've gotten good at this lately after years of being very slow), AMD graphics on 16.4" models, again updated reasonably. OLED screens at least as an option. Physical keyboards, perhaps even with some form of super-thin mechanical keyboard? 16.4" is around 4.5 lbs (I'm letting it gain half a pound of screen, cooling and battery to be more "pro" - this may be optimistic - they might insist on under 4 lbs at thermal cost), while 14" stays around 3 lbs.
There may be 3 models if the 16.4" comes only in OLED - they may keep a continuously speed-bumped 15" in the existing chassis around if the OLED screen is just too expensive to hit a ~$2500 price point by 2021. The new MBP will probably continue to occupy the present MBP price range, from $1500 at the bottom of the 13" line all the way up to $4200 or so for a top-end but reasonable configuration with the most expensive storage upgrades well above that (you can already get a MBP to $6400 or so - wouldn't be surprised if the new one could clear $7000 with the rare storage upgrade)
EITHER
16.4" OLED, 15" carryover, 13" redesign (13" doesn't grow if the 15" has to stay)
OR
16.4" OLED, 16.4" LCD, 14"
MacBook Air - 13" ARM powered (2021 model) well under 3 lbs. LCD screen, butterfly keyboard (unless the new MBP keyboard is both thin enough to fit and not expensive). The Air is the low-end/mainstream notebook, and they aren't going to put anything in it that drives it above $1100 base/$1800 loaded. Note that "loaded" on a low-end machine doesn't include any super-expensive storage upgrades that barely sell - the present $1800 model has 512 GB of storage, and you can go to 1.5 TB for an extra $700 (but you'd buy a 13" Pro instead). Also note that ARM Macs will probably be restricted to the Mac App Store - with some provision for developers to give users credit for software they already own.
MacBook - 12" ARM powered luxury thin notebook. As close to 1.5 lbs as they can make it, OLED, haptic keyboard (which may itself be OLED?). May be completely portless (inductive charging, wireless hub accessory) or may retain one USB-C. $2300 - $3200