I hope they adopt the "Stunning Strike" solution for Legendary Resistances

As we wait for the final PHB UA, I can't help but speculate about the future monster manual playtests, which will give us a chance to revisit mechanics such as legendary resistances.

While most people accept that legendary resistances are necessary to stop casters from trivialising fights, they are widely considered "unfun". The complaint is usually that they separate fights into two distinct goals, with the martials trying to kill the monster, and the casters trying to burn through its resistances. Half the time, the former side wins before the latter does, and the casters feel that they were useless for the entire fight. (Disclaimer: I know this is an oversimplification - casters have PLENTY to do in boss fights).

The UA8 stunning strike seems like a ready solution here. It would align the goals of casters and martials if monsters took a modest amount of damage when they use their legendary resistances to overcome spells (perhaps 1d6 per level of the spell). Luckily, I think the flavour is pretty intuitive. Hitpoints represent an amalgam of health, fatigue, morale etc, and it is natural to imagine that a legendary monster could lean on internal reserves to push through magic effects, losing steam in the process.

I am somewhat worried about buffing casters, but pending some spell power-level changes in 2024, it might be a reasonable solution to a perceived "unfun" aspect of the game.