If you go to the Bungie press room page and browse the screenshots in the Press Kit, there 2 shots of a warlock holding the scythe that actually get a much better view, and looking at the scythes model it looks very much like its a transformed mode of the new glaive
https://press.bungie.com/Season-of-the-Haunted---Press-Kit
Both the the blade material, design of the head (the part the blade itself is attached to) and the red/gold curved talon bit on the backside of the head all match. The shaft of the scythe and glaive also match but the scythe having some extra bits extending from the lower pommel and wrapping the lower grip.
The question then is if this scythe-transform mode is similar to how the current exotic glaives have a transform mode that can be done whenever as long as you have charge OR does it only get this transform mode within the seasonal activity?