We know that at the end of time there is only heaven and hell. We also know that those who have died without mortal sin on their souls don't have the normal suffering of hell but are deprived of the happiness of heaven.
Ergo... It stands to reason that there must be a place in hell where those go who have not committed a mortal sin and are innocent except that they never received sanctifying grace. They are kept from the presence of God but do not have to suffer as those do who lived terrible lives and committed mortal sins and deserve punishment.
It's somewhat disputed whether Limbo is part of Hell proper or a different place, but other than that, this is absolutely correct. While Limbo has not been revealed per se, it's become accepted by the vast majority of theologians, and it does logically flow from the principles you cited.
1) DOGMA: one cannot enter the Kingdom of Heaven and the beatific vision with Original Sin alone.
2) (originally disputed but now nearly-universally agreed upon beginning with St. Thomas Aquinas) Those who have not committed actual sin are not punished for it. (Recall that not going to Heaven is not a punishment, as that is a free gift to which we are not naturally entitled.)
Between these two, it's near universal consensus that there is a place or a state like Limbo. Originally, St. Augustine held that those in category two could end up in Hell, suffering, but with a very mild suffering. This opinion persisted (in the West) for 700 years before being questioned and eventually rejected. Meanwhile, in the East, with the likes of St. Gregory nαzιanzen and others, they already held to a limbo scenario. In fact, St. Gregory rejected Baptism of Desire precisely on the grounds of this principle, that there deprivation of Heaven is no punishment.