Just look at the fan films to see what fans would produce as a series. Yes some are good, but most are collections of fanwank references to episodes, secondary and tertiary (and one-shot) characters dredged up thrown in at random, "wouldn't it be cool if..." plots (that only one person thinks would be cool)...
What WOULD be good is if a production had a pool of fans as advisors and researchers to keep the writers advised of past events and plotlines relating to whatever script they're working on - which the writers could either take to heart or ignore, depending.