Not at all. But that’s based on a (good) guess about what plane will eventually be scheduled for the flight. Especially if it’s far in advance it’s more likely to change. Also, because it’s likely to change, carriers that use both 737-800 and 737-MAX8 (A lot of them if not most of them) likely use similar seat layouts for both, so last minute plane switches aren’t a problem even if everyone has a seat booked. So they could swap a 737-800 for a 737-MAX8 last second and you’d only know when you board it and spot the split winglets.

Boarding is not the first opportunity to know this - the flight plan has the tail number on it.

Apps such as Flighty (and I'm sure others, possibly even those without subscription) will provide access to those well ahead of time and notify you about changes.

It is unfortunate that "changing the plane type" is not grounds to change your ticket however.

If there is a late change of plane (final hours before flight is pretty common) due to technical problems or whatever, then that info may be accessible but it’s not very useful.

It is useful for changing plans if the plane changes days or weeks before departure, but as you say it’s not ground for cancelling or changing your ticket, so buying new tickets every time one sees a 7M8 pop up is going to be really expensive with airlines that have many of them. I guess the better idea then is to avoid those airlines entirely, but that might not be possible at all destinations.

There’s no guarantee that the model of plane that you’ve booked on is the one that’s at the gate.

There’s been plenty of times my plane has been changed out at the last minute due to weather or mechanical issues.