Not sure I like the idea of it being random, but perhaps it could be done based on monster/enemy resistances, i.e. Skeletons take no pierce damage but bash damage, thus on a sword, It's bash value is the damage they take.
Not seen the monster manual for 5th, so can't comment if that's feasible, but IF anyone was to look at different attacks per weapon, this would be my choice, otherwise we would likely be looking at an XCOM type scenario whereby you have cooldowns on particular attacks.
You mean like special attacks with cooldowns? Eeewwww, no.
There's nothing special about grabbing a sword by the blade and smashing your enemy with the pommel/guard like it's a hammer.
Tough you're not always in position to use a specific attack or grip. The enemy won't just stan there and wait for you - you will have to parry/block.
Having a preferred damage type switch option for a weapon (set it to blunt and the PC/NPC will prioritize dealing blunt damage) might be preferable, but my personal choice would be a weighted one. (you won't always do the optimal damage type, but most of the time)
You also have the option of doing all 3 damage types at once (not a fan) or only doing the most optimal type (ok I guess)
