I do like to see that feature, but there are uses for the number of substitutions, i have some while ($regsub(blah)) loops, so please keep this feature also.
A problem might be that there will be 2 optional arguments, the %var at the end and the $regml identifier at the start. This can be difficult to parse if there are 3 arguments given. Maybe the no-%var regsub should get another name or make the last parameter 0 or $null if no %var is present?
