Today, 0x published an interesting and important article about an emerging phenomenon, first seen in PropAMMs, now in UniV4 hooks.
To summarize: malicious makers alternate between very tight and very wide quotes. Tight quotes get the venue selected by the aggregator, but then when the user's trade gets routed to the venue the quote is wide.
Slippage settings (i.e. limit price) protects some users, causing the trade to just fail, but many users set their slippage settings far too permissively. Those users get taxed brutally - the article highlights some hooks alternating between 0 and 18% fees.
(A few months ago, Solana posted an really excellent article about this same phenomenon occurring on Solana aggregators, although with upper-end fees more like 1% instead of 18%. They quietly took the article down a few days later.)
The promise of open systems is elimination of middlemen and hidden taxes. Aggregator spoofing represents a huge hidden tax, and it can only truly be solved by fully-on-chain order routing.
That in turn requires plentiful computation and flexible account access (i.e. no access lists, no pre-specification of touched accounts like in Solana). You basically need a really performant and efficient EVM. On top of that, you need a well-designed on-chain routing protocol. Who's building this?