Tested and inspected in 3.9a #6550. Obsoletes 30 methods and updates 14.
And as Brent says it leaves all 406 Chronology sunit tests passing.  So
I recommend approving this change.  I do suspect there is one bug:
Timespan>>firstDate appears to still be used by
WeekMorph>>selectedDates.  If for example, you do the following:
WeekMorph new openInWorld;  inspect
and then click on one of the days in the WeekMorph and in the Inspector
do 
self selectedDates
you will get an exception