Yes but this is nothing to do with cryptography per se. Most servers can be taken down by a client that finds some expensive operation it can get executed, then sends a bunch of same. The solution implies a generic per-client or per-request resource limit mechanism (which in my experience some systems have, but most do not). This is probably the only good thing about "serverless"/lambda type solutions.

Sure, but an expensive operation sitting as a time bomb within some TLS configs is more easily exploitable than having to find some service specific exploit.

Will Google even do a straight FFDH TLS handshake? I tried with s_client and couldn't find a cipher string that would work (starting by taking the default and just chopping all the non-DH strings out).

Looks like google won't: https://www.ssllabs.com/ssltest/analyze.html?d=www.google.co...