I'm afraid that block rewards are not tainted, because the industry focuses on the majority. Once the miners start moving the money across addresses, here the taint comes.
There have already been several such transactions I am aware of, on both bitcoin and a handful of alts, where someone has made a transaction which sends <1% of the value to another address and pays >99% of the value as fees. There's a good chance that such transactions are by someone trying to create a transaction manually and not really knowing what they are doing or messing up some code they were writing, but there's also a chance that such transactions are a miner making use of the fact that block fees are treated as clean to avoid taint analysis. If such practice became widespread, then you can be sure that blockchain analysis would start treating block rewards as tainted too.
And it also doesn't make sense, even in the head of a conformist: Transactions are picked according to their fee rate, and since bitcoin is censorship resistant, miners can (and should) pick the transactions that pay them the most.
And any miner which decides to censor transactions simply puts themselves at a financial disadvantage compared to other miners which don't. This will only become more apparent over time as fees contribute more and more to the total block reward.