The thing is that Limbo as a theological construct is intended as a merciful approach to deceased unbaptised infants and naturally-virtuous, unbaptised adults. To abolish Limbo is not to move these departed souls to heaven, but to consign them to eternal fire in hell.
At the time of the Jansenist controversy, the Magisterium (I cannot remember which docuмent and have no time now to look it up) declared that no Catholic is obliged to believe in Limbo as it is a theological construct not contained in the Deposit of Faith. However, the docuмent continues, no Catholic may deny the possibility of Limbo.
Yes, the proposition condemned the condemnation of Limbo, asserting that it cannot be declared Pelagianism. I am very much persuaded of Limbo from the arguments laid out by St. Thomas Aquinas, and I believe that the vast majority of theologians in the past 4 or 5 hundred years have been also, though perhaps their motivation for getting behind Limbo weren't theological, but rather part of the emerging trend to undermine EENS dogma. It is still permitted to hold the Augustinian opinion, though it has long been the minority opinion. Cajetan tried to float the notion that unbaptized infants could be saved by some vicarious
votum from their parents, but St. Pius V had the opinion stricken from his works (among quite a few others).
Of course if one applies the Cekadist principles he and many anti-Feeneyites adduce against BoD, since the nearly-uanimous opinion of theologians has been in favor of Limbo for centuries, one would have to conclude that it's now a mortal sin to hold the Augustinian opinion. Of course, the Augustinian opinion was held unanimously for about 700 years at one point, so then Limbo should have been declared a heretical innovation according to the principles of Cekadism.