I don't recall Larian mentioning limiting rests in higher difficulty settings. Or slowing levelling. Or reducing availability of resources.
But im keen to try Hardcore mode! Cant wait!!

"Hardcore mode, then, is where to test your mettle. In this mode, enemy lethality is cranked up to Brutal, ensuring that enemy AI are stronger, will prioritise squishier targets with low AC, and will seize opportunities to go in for the kill. Additionally, many adjustments have been made to the fights themselves specifically for Hardcore mode, with certain enemies receiving additional support through reinforcements, spells, or consumable items."