I have done a list of 6 before, and I have not changed the list.
In the current world of ~7B population, the following has a scale of 1B or more:
Christians (~2.2B according to PEW)
Muslims (~1.6B according to PEW)
Chinese (~1.3B country-wise, and ~1B Chinese-language users according to most sources)
Indians (country-wise ~1.3B, but has maybe ~10% Muslims; Hindu population ~1B according to PEW; and high estimates of Hindi / Urdu users are ~900M, according to Linguasphere)
English L1/L2 users (this may have high overlaps with Christians; but high estimates (also Linguasphere) has it at ~1B L1/L2 speakers)
Adding the early Greeks, it gives the list of 6. The next biggest un-represented group is probably Buddhist, but we are talking the order of half or 1/3 of a billion there; and its textual tradition is more dispersed.
With the recent purchase of Bibek's Debroy's translation of The Mahabharata, I actually have all 6 texts that I can put on my bookshelf! (picture below)