the playerbase being split (or walled off) further by using a promod would have to bring in some pretty hefty benefits to make it worth it. you could pretty easily implement the team comtress optimizations into the game but do any modders know if it would be possible to integrate or mod a pugging system straight into the client?
you could get people to download a promod directly on steam and theyd have access to pugging systems instantly, not sure how doable this is though. imagine you could check a box in the menu to sign up to a pug on certain classes and wait for it to start
you could expand further on this by including proper tutorials and guides for new players, explaining 6s exclusive concepts directly in the game (i.e. valve rocket jump map)