Do you mean give full casters half-caster spell progression? Don't forget, 5e casters actually have fewer spell slots than their 1e/2e versions do.
Make it so a slot can only be used to cast a spell of its own level, period. No up-casting, no down-casting, no combining slots. You're out of 2nd-level slots for the day? You ain't casting any more 2nd-level spells until tomorrow no matter what you do. (the biggest thing that this - very intentionally - impacts is Clerics spamming cures, but it limits Mages as well)
At the same time, however, bring back the idea of many spell effects - range, AoE, and most notably, damage - scaling with caster level.
I've never been a fan of wild magic myself since it is often too lolrandom for my tastes.
Random is the point, at least the way I rationalize it: when you're trying to cast a spell, the first step is to gather up some magical energy. If you're interrupted during casting that energy is released in a manner unintended; and while it might just dissipate harmlessly it might also manifest as just about any effect you can dream up.
But I could definitely see some sort of backlash. In fact, backlash (or a wild magic table) could be done per magic school. Getting a fireball because you miscast silent illusion doesn't make sense to me, but having your illusion come alive, having it duplicate you but not be under your control, turning you into an illusion, etc., would make sense.
Yeah, that could work too, but it seems a bit limiting. Wild magic is perhaps the one place in the game where I don't want things to make sense; and having an interrupted illusion generate a cure (or cause!) serious wounds on some random bystander is fine with me.
I've seen a lot of suggestions for something like this over the years. Usually it involves Con indicating how many Wounds you have. What would you have as the hit point-to-Wound ratio? Or would it be that only certain types of injuries inflict Wounds?
The way I do it, and have since forever, is way simpler than that.
Everybody - including commoners etc. - starts out with a small number, usually between 2 and 5, of Body Points (BP); one's species determines the die size rolled for this and one's Con sets a floor but does not otherwise adjust the roll. Barring very rare circumstances such as outright loss of a limb, one's BP total never changes. The normal hit points you get for your class and levels are Fatigue Points (FP) and go on top of your BP to give your total hit points. Death is at -10.
When taking damage, once you've gone through all your FP you start taking BP damage - there's no specific Wound-causing system here - and BP are harder both to rest back and to cure up (BP cures roll smaller dice). If you go below 0 you can't be magically cured* above full BP at all for a length of time set by how far down you went, but can slowly rest back FP.
That's the short form of it.
* - except by a full
Heal, which cures everything.
