If by protocol you mean base layer, then yes.
If by protocol you mean application level but interoperable, the Samourai's postmix tools already fit the bill since they are interoperable with Sparrow's.
You can do a Stonewallx2 between Samourai and Sparrow today. No central coordinatot 

 what’s the advantage of not having privacy on the protocol layer? why rely on applications that are not part of the bitcoin protocol? 

 * You needs hard forks
* there's a tradeoff where the transactions are largee. An average monero transaction is 3x the size of a bitcoin tx