This is a very bad idea.
I won't dwell long on the idea of saving only while resting in a game that is 90% rng based.
Did you miss the mention of the " for ironman mode only"?
However, resting in a given location is pointless because there is a fast travel in the game from anywhere on the map. Changing it to specific places does not make any sense, at most the player will spend 30 seconds to get back to the place.
That way, it might as well stay as is.
Limiting rest to some stage in the story makes even less sense because the game is fully non-linear, which means that the developers are not able to predict in which order the player will fight.
Something like this is turning off the problems.
This makes sense and is fully justified in the story driven rpg its gives a sense of time and progress of the plot that it is not felt right now. The game is not linear true, but it divided into zones and has important steps in plot, like example after the first visit to the Druids Grove(lets say after a dialogue with the Kanga) another camplace is unlocked. Another unlocked...lets suppose after the Hag den. So on.
Other than short rests requiring supplies, these are all things that you can do on your own, if that's how you want to play it. I have missed out on plenty of comp dialog/comp story advancement because I don't "abuse" the long rest system. I am, again, more concerned about adding some kind of notification about those, than limiting what someone else can do.
This is just a reasons why I suggest campplace system. You have passed some stage in the plot, you receive an alert and need rest. Right now it is too messy.
And from the point of view of limitations and chalenge, I also see its as logical solution, you have a certain amount of resources(spells and skills) and you must use it carefully to pass some part of the game, before next chekpoint/rest will be unlocked.
