A thought, because of all the folks asking for volume limiting: if you're not into DSP, it might be easier to simply add a point in your audio output flow for AudioUnits and let people use one of the existing limiters for it - Apple just straight up includes one on every Mac in the AudioUnits library - or write one specifically and include it.
This would also allow not just limiting but EQ, compression or even simulated tube warmth if people wanted that. (Or, y'know, running everything through autotune and a bit crusher if they're psychopaths. :-D)
I've never coded in Swift but I imagine adding a point to route through AudioUnits is probably not hugely difficult and iirc Apple has example code for doing it, at least they used to.
Keep up the awesome work, either way!