If you were to rebuild 4chan today...

...what type of data storage layout would you use?

Would you remain with a mostly flat file layout and what technologies would you use to implement such a layout?

Personally I'd go with JSON files and some random JSON library for writing, cache and reading stuff.

Personally I'd go with JSON files

Too much work. I'd just use Postgre SQL reliable and fast enough solution with minimum work. Who the fuck wanted to do anything extra in web development hell?