If they beat at different rates...they can't do it simultaneously...
...but I know what you meant to say.
I assume you plan to do this in the digital domain...I mean, it would be difficult to do it with real metronomes, and I doubt you would find more than a handful of different types to use.
Anyway...it's as simple to do digitally as the amount of time/effort you want to put it.
You can put one metronome on each track of a DAW (record/bounce it to the track)...each set to a different BPM.
Of course...I don't see you running thousands of tracks simultaneously...so you might have to do them in chunks of a few dozen or whatever your DAW allows, and then sub-mix down to one...and keep repeating for as many times as you want to keep adding new BMP tracks, or until the sound becomes the noise you are looking for.
All that said...
Do you mind explaining why something like this is even interesting?
I mean...you just want to be able to say..."It took 500 metronomes before it became unidentifiable noise"...or some such thing...?
I actually don't think it will take even 500, especially if the sound (not the BMP) of each metronome is the same. The individual beats will start masking each other pretty fast, IMO. Of course, you could use different sounding metronomes...but even that would "blur" not much later than if they were all the same metronome.
So...you joined the forum just to ask that?
I get the feeling this is just a joke question...but hey, if you're serious...knock yourself out, and let us know how it comes out.
Oh...you wouldn't by any chance know a guy called "whome" or "mr average"...?