If I recall correctly, the 2001 ICFP contest was won by someone who happened to have done their thesis on the contest problem. :-)

That the task description is only posted at the start of the competition?

I mean, if you design an esolang for the competition task and implement an optimizing compiler that's faster than any general purpose language out there, that absolutely feels like something that should be rewarded by the spirit of the competition! So it's okay that it's allowed by the letter of the competition, too.

Nothing, if it helps you with the challenge.