The three musketeers have always referred to J-10, J-16, and J-20.
There is no way the J-11 and J-16 are counted separately. They said a 4th member is "joining" the triad. J-11 and 16 are already in. J-10 is already in, J-20 already in, therefore the 4th member is someone new. It can only be refering to J-31/35.
? J-11 and J-16 obviously have to be counted separately, because they are entirely different aircraft with entirely different capabilities.
Similarly, it is J-10C specifically that is associated to be much more capable than J-10A/B.
The reason why J-10C, J-16 and J-20 were considered the so called "three musketeers" is because they emerged at a similar time to one another and could significantly leverage each others strengths through use of effective datalinking at a level that other previous aircraft could not, this being individually but also collectively far superior to past fighters.
Coupled with the facts where:
1. There are no more new variants for the J-10, J-11 and J-16 series;
2. There are neither news nor rumors of a 3rd 5th-gen fighter (J-20B isn't exactly distinct enough from J-20A to become its own "musketeer"); and
3. 6th-gen fighters are still around a decade away -
Then I think it is reasonable to conclude that this "4th musketeer" could be an unofficial hint that the land-based version of the J-35/31, i.e. CTOL J-35/31 will be inducted into service with the PLAAF in the near future.
Therefore, I think the following questions on would be:
1. How many CTOL J-35/31s does the PLAAF need? and
2. How fast can Shenyang produce those J-35/31s (and is there any visible expansion of Shenyang's production facilities recently)?