>> IMO it is would be much better to map the existing repeat command to a 
>> single keystroke, it would make any command repeatable without changing 
>> anything else, and it already handles universal arguments.  I think C-= 
>> would be the best key for this
>
> FWIW, one of the reasons Zhiwei gave for his initial "C-x o o o…" 
> proposal was:
>
>> 2. Reduce the probability of RSI
>
> I'm assuming this would stem from having to hit Control less often.
>
> Not that we couldn't have both a repeatable C-x o *and* bind C-= to 
> repeat; I merely want to point out that C-x o C-= wouldn't fully satisfy 
> the OP's requirements.
>

IIUC, what the OP said is that hitting C-x o multiple times is painful, 
because it requires releasing and pressing the control key mutiple times. 
For example C-x o C-x o C-x o C-x o requires pressing and releasing the 
control key three times.  With C-= bound to "repeat", you could achieve 
the same effect with C-x o C-= C-= C-=, which requires releasing and 
pressing the control key only once.  You could also achieve the same 
effect with C-x o C-= C-= C-= C-= C-- C-=, which also requires releasing 
and pressing the control key only once.