Both IRR and TWR are annualized specifically to enable comparison / some sort of common basis for different investments.
Internally the rate is computer per day and then annualized, so on the surface it seems relatively easy to implement the proposal.
However, I think that this would open a moderately-sized can of worms.
When people say "monthly rate of X" or "quarterly rate of X", they usually mean the rate that is the same every month (or quarter, or any other period, like week).
Under this proposal, however, hledger would be reporting a rate over, essentially, "a period of N days". So for investments that grow the same amount every month, reported "monthly" rates would be different as different months have different numbers of days (and same for quarters). So it will not be a "monthly rate", but rather "a rate for the month of Jan 2022", which is a rather different beast.
So it would be surprising and highly unorthodox, but at least the behavior would be consistent: -M and -p '1 month' would produce the same results, as well as -Q and -p '3 months'. This would have to be caveated in the docs, and I bet that the resulting figures could be rather surprising (and potentially rather useless) for end users - at least on the small enough intervals (month and below).
However, if you want -M and -Q to report monthly and quarterly rates in their usual meaning, they could, of course, be special-cased in the code, but now -M and -p '1 month' will not be equivalent. Special-casing monthly and quarterly cases also opens the door to the discussion whether they should be computed allowing for compounding or not (that is, should the reported monthly rate be the rate that yields the equivalent annual rate with compounding or without).
So in my opinion it is best not to implement the change as proposed.