The only spells that would have a bad interaction with this are spells that forcibly move an unwilling target and are not restricted to toward/away from the caster, and thus can move targets upwards.
The only spells that come to mind here are Bigby's Hand and Telekinesis.
Bigby's Hand could drop a grappled target from 60ft up, then move down and re-grapple to cause 20d6 (70) damage every other round. Consider that its normal expected damage is 18 per round, and this tactic would approximately double its effectiveness.
Telekinesis has a similar issue, moving a targeted creature 30ft upwards each round and dropping them every second round for a similar 20d6 per two rounds.
The biggest issue here is really that both of those spells are very reliable, as they target Athletics/Acrobatics and Strength instead of AC or Saving throws.
Otherwise, you'll also have to be wary of some grappling character builds - dragging a creature up the side of a building could easily become more damaging than simple attacks at a relatively low level.
For example a level 3 Thief Rogue could attack someone for ~14.5 each round with Sneak Attack.
Or they could grapple and drag them 30ft per round up a building/cliff/etc, dealing approximately 20d6 damage every third round (plus another attack in the middle round), again nearly doubling the expected damage output.
All in all, the two spells mentioned are the most problematic parts as they can be tacked on to many spellcasters, and don't require an unorthodox character build that specifically takes advantage of this houserule.
But consider also that in a world where a 60ft fall is lethal to most spellcasters under level 12, every spellcaster capable of knowing Feather Fall will know Feather Fall, and mitigate the increased danger that way.