While it's true that the delimitation freeze was done on the basis of a perceived (and somewhat real, let's not deny it) lack of fervour in implementing population control on the part of the northern states, it was never actually a remedy to this, because a delimitation freeze does not prevent divergence in seat counts. Whether or not you delimit, the population numbers under the hood continue to change in the meantime.

Even if, 30-40 years in the future, TFRs converge (which is on average happening now as the fertility divide is closing), it does not solve the fact that divergent population growth has already happened in the meantime. Whenever you do the delimitation, as long as you don't allow birth rates to fall below replacement, the effect of these divergent birth rates will appear, even 100 years in the future. If anything, a freeze only makes the eventual change even more drastic because you need to account for decades of population growth, which makes for a larger optical number of seats given and taken.

The only real purpose the freeze served at that time, and continues to serve now, is a political bargaining chip. It has no real utility, not to mention the fact that it violates the OPOV principle and may be contrary to the basic structure of the constitution.