Miners employing parallel validation do not fall victim to extended time validating blocks containing aberrant large quadratic hashing time transactions. Instead, they orphan such blocks. By continuing to mine and validate on other threads while the validation of the aberrant quadratic hashing time block runs on one other thread. Miners who continue to make blocks with such transactions will eventually bankrupt themselves. All without doing any damage to the network. Problem solved.
What implementation includes parallel validation? Oh yeah... BU does.
Given the massive amounts of ram required by ultra large transactions that are heavy in sigops that would be prone the quadratic scaling laws, validating yet another block in parallel is an excellent way of using even more ram. High ram servers with 256GB may be able to cope temporarily with it but normal machines and even normal servers will likely run out of memory and kill bitcoind.
Which implementation has had out of memory issues already? Oh yeah... BU did.
You don't think the significant mining pools can afford one large server each?
And that's your solution? Have only 10 nodes that can stay online worldwide during that parallel validation period and crash the remaining 6000+ nodes worldwide at the same time?
Yes. Anyone who wants to be a central element of a multibillion dollar system is going to have to buck up for the requisite (and rather trivially-valued, in the scope of things) hardware to do so.
Bitcoin's dirty little secret is that non-mining nodes provide zero benefit to the network at large. Sure, operating a node allows that particular node operator to transact directly on the chain, so provides value to that person or persons. But it provides zero utility to the network itself. Miners can always route around the nodes that do not accept their transactions. Miners don't care whether non-mining nodes accept their blocks - only whether other miners will build atop their blocks.
And the number will not be ten - it will be many more. As again, anyone who wants to be able to transact directly upon the chain in a trustless manner will need to buck up to the hardware demands.