As commented in thread of "rounding integers" , I have opened a PR
 for fully supporting formatting integers using "number_format"
without any precision loss.
Additionally, on working on it, I noticed a possible integer overflow on
|$decimals |argument of the current function. As this is at least an
internal API break I have opened a separate PR  as fix.
I hope for these PR's no RFC is required as it does not break PHP API.