GT Sport in particular has moved in the direction of less time doing "stuff" and more time actual racing. I seem to recall an interview with Kaz on here referring to that.
One thing to remember is that they need to attract gamers under 30 to keep the franchise going in the future. And, like it or not, many of those gamers are playing games on their phone or tablet as much or more than they do on their consoles. I think PD/Kaz believe(d) that the main competitor to GT Sport wasn't going to be the next Forza motorsport or Horizon, it's more like..
https://www.geek.com/games/forza-street-makes-microsoft-racing-game-mobile-1783246/
Personally, I think that was a mistake by PD and they were surprised by the resulting backlash. So the next game is likely to be a bit more traditional but somehow it's got to fit with esports too.
Personally, I think the suggestion of "stock bop" cars for online but with tuning added for offline would be the best solution.
They could even address the wish of some to have all cars unlocked by making them available in arcade mode but only the stock bop ones.
But as someone said above, microtransactions is around forever more, unfortunately. If all the cars are available from Day 1, there's nothing for you to buy that's going to generate anywhere near enough revenue to replace buying cars.
The one good thing in all our favours could be the obvious commitment of Sony and PD to esports which seems to growing not reducing with the Toyota sponsorship. They can't have "pay to win" microtransactions as that would bugger up the esports. But that also means they can't have paid DLC post release because that will split the online community and esports too. So, I think the situation will stay similar to what is now.
The thing they should do though is equalise the online and offline layouts. There is more than a dozen races in GT League that can get you about 1m credits or more in an hour (F1 car, Red Bull, Nostalgia etc). There should be the equivalent online too.
In the end, I don't know the exact percentage but 90% of the cars in this game can be purchased in an hours gameplay in GT League which I don't believe to be excessive.
Improve online payouts and do something about the unicorn cars e.g. make them winnable through achievements (levelling, trophies or something like that) and you have a game that will work for the majority I think.
I think using the Mileage Exchange for upgrades could be a good idea if they develop it on an ongoing basis, e.g. keep adding parts for new cars as they are released and new parts for existing cars, or if they have a large selection ready at launch. That could fit with upgrade bundles too. 1,000 MEX for brakes, 500 for exhaust etc, maybe 5,000 or 10,000 for an automatic upgrade for those who don't want to "tinker". It's worked in a similar way successful in other driving games.