The idea of Surface Effects is interesting, but on this scale it isn't very D&D and creates chaos with both the balance and how the playerbase expects a 5e game to behave. HOWEVER, what would be interesting is to have surface effects trigger off a natural 20 crit roll for spell attacks.
SO, no surface effects on firebolt, but on a crit, a surface effect triggers. It would make a crit even cooler/more interesting, and it would cause less balancing issues. A player can't PLAN to get a crit, so the game would largely play like 5e but would get some spice mixed in to make combat less predictable.
