This is a little silly.
If we took out the mentions Minion, Elite, Solo, Brute, Skirmisher etc. as well as the level of the monsters, do you know what we'd have? The AD&D monster compendium. And no one would be wondering the implications of a minion. They'd just say: "Oh, look, that monster is only worth 25XP and is really weak. Let's put a boat load of them for one encounter, it'll be fun."
And what if some ultragrognard still playing AD&D and suffering from Monica Geller syndrome decided to label each monsters and formed a minions category formed of things like 1 HD goblin and Orcs? Would it create the same type of debate even though we managed to survive the 80s without knowing that a kobold was a minion?
Thematically, minions can be anything. Mob of peasant, throngs of vampire spawn, royal guards... the only common link is that there is likely to be tons of them attacking at the same time.
Mechanically, minions are low HP creature that you can swamp the PC in. And these minions have always existed in every iteration of D&D.
There is only two novelty about them, and I love it : First of all, now some of them have been designed to be a challenge for PC above level 3. Secondly, and this is a guess based on the few mionions revealed so far, they all have some sort of mob bonus that makes extra dangerous until you have thinned them out.
For example, I just love how the Vampire spawn are like pirahnas. Consider this; first column is the number of spawn, second is the maximum damage they can do to the same PC they are surrounding, third is the same against a bloodied PC. I find it just hilarious and thrilling. I'm eager to use them and watch the expression of the players as they realize the implications. Weeee.
1 3 5
2 12 20
3 27 45
4 48 80
5 75 125
6 108 180
7 147 245
8 192 320