I have explained the whole idea with a proof of concept in this link: https://medium.com/@prayankgahlot/post-mix-usage-using-multisig-and-cpfp-e6ce1fdd57a1

Does it make sense to add such options in bitcoin core wallet and how is the overall idea once we have taproot because for now people can check if the tx involves a multisig address?

Reading Peter Wuille's reply here it seems taproot will improve privacy for multisig: 

Looking for some feedback to work on this idea and don't want it to just remain an article on medium. 

Thanks

Prayank