With JWE3 they did not release all creatures from the previous game at launch because I imagine they have to code all the family units, so they prioritised only a part of the roster, but the latest update introduced a new family unit for free which makes me hopeful that, at the very least, the rest of the animals present in previous installments will be available for free while they add other new animals through DLCs as they always did (if they release the hybrids behind a pay wall for the third time and people still buy it at this point the fault is of the audience).
They have explicitly stated that the JWE2 base game animals that are still missing from JWE3 will be added at an expected rate of one a month from January 2026 at no extra cost (and they attributed the delay to the time needed for developing the family units just as you say).
It was very much specifically base game animals and no mention was made of JWE2 DLC animals that are still missing so one has to suspect they might be in paid DLC once again if they reappear - or at least they're keeping their options open.
It would not surprise me at all if PZ2's launch roster is a similar mix of PZ1 base game and DLC animals.