I recently came across this post on Reddit, and got to thinking about the viability of a newish mechanic, where the strength of the dice used determined the AC before rolling. For example, a lower end NOM (non-Newtonian Ooze Monster) may have a base AC of 8 plus 1 for every d6 or d8 rolled for damage, plus 2 for every d10 or d12. A level 3 party with a barbarian wielding a great axe would encounter this NNOM with an AC of 10, whereas a rogue in the same party would see it at 12AC when sneak attacking (11 if they're using a weapon with damage of 1d4). Different NOMs would have different resistances and immunities as proscribed by the adventures needs.
Calculating the CR of an encounter with a NOM would require a bit of extra math as well, as the AC would depend on the expected damage output of a typical party at that level.
I'm concerned that this homebrew will horribly unbalance my campaign and cause my players to rage quit.
Does this homebrew seem viable and balanced(ish)?