Outside of limiting taproot script length (which could have its own follies we as non-devs haven't considered), anyone who believes the "spam" can be stopped by fine tuning or placing certain limitations within Core is sorely mistaken. The
exact same argument was happening around the launch of Counterparty in early 2014, and the Counterparty devs told the Bitcoin devs, fine, do what you want, we will find ways around it. There's a number of different ways to add arbitrary data to transactions, and there always will be.
Basically Luke-Jr is saying we should have a model of explicit whitelisting where people ask permission first to use Bitcoin. Right now that wouldn't be one patch, it'd be two patches: Counterparty and Mastercoin. Very soon it'll be three patches as Colored Coins adds decentralized exchange functionality, and probably soon after that four patches when Zerocoin is deployed, five once the guys doing secure multiparty computation with Bitcoin release their software, six for... You get the idea. On top of that from technical perspective writing a general purpose patch to distinguish even just Counterparty transactions from "spam" is impossible without having access to the Counterparty consensus state. Sorry guys, but Luke is either foolish or trolling you.
Some things never change...