There are several papers about how to stop DDoS by using cryptographic
puzzles.[1] The core idea is to give the abuser some algorithmic work he
has to solve, thereby forcing him to waste processing power, and then to
slow him down to a manageable level.[2] That only work if you are the
target, and not some intermediary are targeted.
Could it be a solution for the WMF servers?
[1]
http://d-scholarship.pitt.edu/24944/1/mehmud_abliz_dissertation.pdf
(just a random pick)
[2]
https://searchsecurity.techtarget.com/answer/TLS-protocol-Can-a-client-puzz…
(about
TLS, but can also be done at the application level)