I'm one that feels that this is a game and shouldn't be too unduly burdened by certain aspects of reality.
I mean maybe there needs to be some attention paid to the challenges of swapping a V12 into a Fit, maybe, but not the rarity aspect so much.
Games by their definition imply some amount of restriction, or rules if you will, and it's by exploring these rules and mastering them, if not circumventing or otherwise besting them in inventive ways, that all the entertainment is found.
And these very fora are full of examples. Speaking of masochists, I'm reminded of those tortured souls who attempted to lap the Nordschleife in the Benz patentwagen in GT4. No trophy for that. As it should be.
And that's really the point. Make things flexible and accessible so that we can tailor our own challenge, assuming we're actually disciplined in any way. Not that it matters, it's a game, have fun!
I did think though that taking a car and removing its engine might be a bit heretical to PD, given this is about worshipping cars and collecting all of them and ultimately not letting them "die" in a sense.
I mean, if you remove an engine from a car, does its soul go with it? Clearly that's contradicted by the very presence of swaps in the game in the first place. But it does present a logistical problem: what happens to that engineless husk? How do you stop engines littering your collection? Etc. It needs to be comprehensive and robust.
Maybe for now it satisfies the lootbox criteria for Papa Sony at launch, and it can be patched to be more sensible at a later date. I feel PD have form on this kind of thing, e.g. something like exclusive pre order bonuses or some other such cynical nonsense, only for them to be patched in for all to be earned at a later date (I don't exactly remember).