I understand the argument of both sides - Discourse offers options for replacing a short reply by an emoji which was not available in the old forum. As soon as everyone got used to it I am sure most of the very short replies will disappear. On the other side these options do not cover all possible cases as pointed out in different posts before which makes it necessary to type some nonsense characters just to cover the minlenght requirement.
What I dislike most with the minimum length ist the arrogance behind the rule. Someone decides to fix a willy-nilly minimum lenght and every user has to follow. OSM is an open project and it would suit the forum well to be open enough to allow its users to decide what they want to write and in how many words.
The “tons of irrelevant notifications/emails to dozens or hundreds of people” suspected by @nukeador have not been a real problem in the old forum as far as I have noticed. There is zero proof this will happen in reality, it is just an assumption. If this should really grow into a serious problems the introduction of a minimum length could be kicked off. Until there is no reason to justify a limit at all. That is why I do not see the need of any minlenght at all at the time being.
PS: If the argument pro minlength is to avoid irrelevant and annoying short posts in public discussions why is there a minlenght for private messages as well …?!?.. this is nothing but nannying imho.