Wasabi used to depend on Bitcoin Knots but since v2.6.0 that's not the case anymore. Bitcoin Knots provided an RPC feature that was not available in Bitcoin Core: GetBlock with previous outputs (verbosity 3), which was necessary to create the Wasabi custom compact filters without needing to keep a UTXO set as it did in previous versions. Additionally, both client and server made use of another exclusive RPC, GetMempoolInfo with fee rate histogram, which allowed Wasabi to estimate the fee rate better.
After Bitcoin Core merged the PR that extended the RPC GetBlock to provide previous outputs and the fee histogram was made optional in Wasabi, there is no more need for Bitcoin Knots. These changes were done long ago, much before the current discussion about OP_RETURN, and the reason behind them is purely technical.
Getblock with previous outputs is good. Now I can do things like checking the source address of the transaction without having to store several hundreds of megabytes of UTXOs in-memory, many of which are just OP_RETURNs or some kind of Ordinal anyway.