Optatam Totius 6 handles a timely topic:
With watchful concern for the age of each and for his stage of progress, an inquiry should be made into the candidate’s proper intention and freedom of choice, into his spiritual, moral and intellectual qualifications, into his appropriate physical and psychic health-taking into consideration also possible hereditary deficiencies.
The recent Vatican instruction only makes sense in light of this statement and applied evenly to any potential priest. Do SSA candidates have the right intention? Are they healthy in every way?
Also to be considered is the ability of the candidate to bear the priestly burdens and exercise the pastoral offices. In the entire process of selecting and testing students, however, a due firmness is to be adopted, even if a deplorable lack of priests should exist, since God will not allow His Church to want for ministers if those who are worthy are promoted …
In other words, it’s not a cause for desperation.
… and those not qualified are, at an early date, guided in a fatherly way to undertake other tasks. The latter should also be given sufficient direction so that, conscious of their vocation as Christians, they might eagerly embrace the lay apostolate.
It would seem that an embrace of the lay apostolate (the baptismal apostolate, if you will) should be in evidence before a person enters seminary.