Depending how you count it in canon, there are between 40 and 160 students in a Hogwarts class, per year, from all 4 houses combined. 1/4 of them are purebloods, so that's between 10 and 40 purebloods per year. If wizard families have on average 2 children and start having kids when they're 30, then we'd need to account for between 150 and 600 pureblood nuclear families at the time of the story. Arbitrarily assuming that a pureblood family should have about 3 branches at a given time, that's 50 to 200 pureblood family lines to classify.
How many noble houses should there be? According to this page, there appear to be 498 existing hereditary peerages in the UK. While Magical Britain isn't proportional in size, I don't see any reason why it should be. I rather think of it more like the SCA.
My feeling is that in the beginning, all the wizards got to be Lords, and you're a pureblood if you can trace your line back to them.
My feeling is that in the beginning, all the wizards got to be Lords
The SCA can get away with having an arbitrarily large proportion of lords and ladies because they don't need any real assets or authority. But if everyone is a Lord, then for practical purposes nobody is. You end up with a Too Many Chiefs, Not Enough Indians situation. A Lord needs to be able to have servants.
It's silly to assume that Magical Britain has a similar proportion of peers to nonmagical Britain, that would imply fewer than four peers in the entire country even by the most ge...
Warning: As per the official spoiler policy, the following discussion may contain unmarked spoilers for up to the current chapter of the Methods of Rationality. Proceed at your own risk.
Assume HPMOR was written by a super-intelligence implementing the CEV of Eliezer Yudkowsky and assorted literary critics. What would it have written differently?
... is what I want to know, but that's hard to answer. So here's an easier question:
In what ways do you think Eliezer's characterisations/world-building/plot-fu are sub-optimal? <optional> How could they be made less sub-optimal? </optional>
(My own ideas are in the comments.)
To put it another way... Assume a group of intrepid fanfic writers in the late 2020s are planning to write a reboot. What parts of Eliezer's story do you think they should tweak?
And just to make sure we're all on the same page: Eliezer isn't going to go back and change anything he's written to bring it in line with anything suggested here. This is purely an "Ah, just consider the possibilities!" thread.
... which means that we can safely suggest drastic rewrites encompassing 30 chapters or something. Or change fundamental facts about the world.
(Exercise due restraint on this one. Getting rid of the Ministry/the Noble Houses/blood purism would probably turn the story into something completely different; this isn't what we're trying to do here.)
With that, let the nit-picking begin!!