A very bad idea for many reasons, and other people have posted them.
Lemmy.world being large is self inflicted, chosen and promoted by themselves. It’s not a surprise that having 100k users pick the same server is a bad idea if you want to keep the costs down.
Their size is creating many problems in the Lemmy fediverse now, because almost all communities and users are on one instance. Anyone not federating with Lemmy.world has no content.
This is why their decisions matter very much for everyone now also.
Funding the fediverse should be done by individual instance owners who wants to support a healthy network. This is no longer possible if you let your instance become super big, and that’s why it’s a mistake to become super big.