BoD is also implied Pelagianism, which St. Augustine realized after battling the Pelagians.
Is the desire itself salvific? Is it meritorious unto salvation? No; to say so would be Pelagian heresy. God gives salvation freely. So what exactly is the role of this desire vis-a-vis the reception of the Sacrament? In point of fact, it's nothing but a SIGN that the soul appears to be cooperating with the will of God. Presumably God will give the Sacrament if the soul perseveres in this cooperation. This implication that it would be unjust of God not to save someone who had the desire for Baptism, it implies that this desire is meritorious or efficacious in and of itself unto salvation. That's Pelagianism pure and simple. To imply that it would be unjust, or unmerciful, for God to withhold salvation from someone who appears to be so cooperating is to pretend that one can see into the internal forum. "Look at that devout catechumen, who wanted so much to be baptized, and yet was cut down before receiving the Sacrament." [how do you know the internal forum state of that person?] vs. "that scoundrel lived a sinful life but was baptized on his deathbed." This is the "thinking" (aka emoting) that led to people beginning to theorize about BoD during the time of St. Augustine, and he rejected this reasoning as leading to a "vortex of confusion" ... which is most certainly is because it's extrapolating from a presumed knowledge of the internal forum to theological speculation.
"What if there were such a devout soul, ...." Well, what if? We don't know that there EVER has been one whom God did not bring to the Sacrament.
BoD is a vortex of nonsense and confusion, which has never brought any good fruits, only bad ones. Our Lord taught that we would know things by their fruits, and the fruits of BoD theory are absolutely pernicious. There's no need for it, no proof that anyone was ever saved by it, leads very easily into the heresies of 1) Pelagianism, 2) denying the necessity of the Sacraments for salvation, 3) invisible Church ecclesiology, and 4) effective denial of EENS.