That hammer and nail analogy doesn't work. It's self-limiting. A music keyboard puts out MIDI, but that isn't the same as saying that MIDI implies a keyboard controller!
I challenge the point about serial control, it's probably no more able than MIDI is for sending signals for laser controllers to use, and is harder to implement, excepting that many computers still have serial ports, a point which does nothing to address the ADC conversion for your control inputs.
It's also why I challenged this idea that Pangolin's use of MIDI is all you need to consider, it almost certainly is not. MIDI is always more diverse than any single adaptation of it.
First, look carefully at what kind of signals we should consider using it for. Obviously it is NOT analog waveforms. Neither serial OR MIDI could send those, you'd have local waveform or other fast signal generators in the laser controller itself. MIDI isn't for the neural feedback that controls muscles, it's for commands like 'turn left', 'step back', 'go this much faster' or whatever.
It's obviously NOT limited in what control messages can be sent. All it is is a protocol for sending control and data bytes for those controls, using cheap well-established and reliable hardware.
If you want to speed up the LFO in a Lissajous generator, you turn a knob. Obviously the LFO is an oscillator that uses gain and feedback to make it run, and this is local, but there is no reason a slow control can't tell it what speed to change to. This order CAN be sent through MIDI, it can be sent that way with more response than you can put into your hand to turn the knob.
And the knobs can be fitted to your own customised control surfaces. Buy Doepfer's 'Pocket Electronics' or other simple boards to make whatever glorious kind of control surface you can imagine. Use a downloadable freeware program Doepfer provide to program your own MIDI control codes for each knob and switch if the inbuilt codes and preset control arrays aren't ideal already.
The whole point of this is that it is NOT limited! Far from it. It's actually the only way that DIY projector-building people can go this far. Any other way, they'll be tied to the coat tails of those who can prototype and market a viable system from raw components. Doepfer did what they did to enable people to build their own analog synthesizers. We've already established in many discussions how close such control is applicable to laser control (that sound card thread, for example).
What MIDI allows is a complete fly-by-wire system. Most of the possible nasties like data jamming and panic messages to shut things off have been developed for tens of years, for a an industry that includes expensive large live shows. There aren't many systems better suited, and probably none cheaper or easier to use.