This change ca645a9 seems to cancel the effect of retrocycle when using custom reviver, since resolved value is strigified, than parsed again.
For example if I want to let $jsan deal with Date values in retrocycle and additionally use custom reviver for some custom type, Date value will be stringifed once resolved and then parsed into string, so I end up with string instead of Date.
Is the idea of this change that you should either not use reviver at all, or to use reviver for all the values, including the ones retrocycle can process?

P.S. This line is useless after this change since needsRetrocycle variable is never used.