For the record I am so on board with curved-rail variants. Just so long as I don't have to write the code
BTW the entertainment value of this type of thing can be assessed in Transport Fever (a pretty nifty lookin' game I would probably play if Factorio didn't consume all of my video-game attention-span... Transport Fever is to Transport Tycoon as Cities: Skylines is to SimCity, if that makes any sense). In that game, too much track curvature will absolutely slow down your trains, limiting throughput, and so on... the whole can people are kicking around here is in that game. And, well, that's a game about trains in a way factorio probably will never be... but I do think the net effect of that type of "technical train annoyance" is positive there (I don't have meaningful direct experience with the game, though, except as a spectator).
I will admit that it's quite amusing, sometimes, watching Factorio trains whip around corners at completely unrealistic speeds. Just as it can be liberating not to have to worry about power for transport belts, nuclear safety protocols, or bots running into each other, there is a kind of platformer-physics charm to the way Factorio trains will predictably traverse any insane route you can build for them like it's a cakewalk. It allows one to focus on other things, I guess.
But I do think the current game-engine limitations for trains do sometimes make the factorio train mini-game feel a bit tacked-on. Like, I don't know, a train-car is just a super high-capacity bot with a hit-box and configurable routing, or something.
That's a super-critical viewpoint, though. I fully enjoy Factorio train stuff, just as it is, and completely understand why it doesn't make sense to be tearing up the train grid or attempting to wedge more and more flexibility into it, at this stage of development, or, maybe ever. Admittedly, I clearly don't fully qualify as a hard-core balls-out obsessive rail-nerd. In fact I'm not completely sure why I'm even posting here... I guess to provide a "normie" perspective?