May 2nd is supposed to be the last day your local Ford dealer can order a 2016 model. My Ford contact is telling me that the order bank is about full so that date is going to be pretty firm.
Advantage of ordering a 2016 versus a 2017? You will get at least a $2100 rebate on it plus any added incentives when the Transit arrives at the dealer. Unless you want some of the new options coming on the 2017 like the heated seats, restyled console, and the power passenger side step there will be no changes in the main configuration of the Transit. There is a proposed MSRP increase of 2% on all 2017 models coming out to account for the additional cost of ALL the current model updates and recalls.
Ordering a 2016 now and it will be built by the end of July or earlier; ordering a 2017 after next week and you are looking at it being built close to the end of August/first of September.