I do believe I've heard that Pumpkin is the next Season Plant. After Pyre Vine's season ends, Pumpkin's will start, which will also coincide with Food Fight (PVZ2's Thanksgiving event). Pumpkin has probably appeared in the Almanac early because ever since Blastberry Vine, they've been providing "Early Access Bundles", which let you straight-up buy the Season Plant and immediately get it unlocked, instead of having to build up a tournament Season score.
Me, I'm just going to wait and get it for free from the scoreboard. I'm sooner interested in Parsnip, which should become available to buy during Food Fight. It'll be great to have another melee attacker to join up with Bonk Choy, Wasabi Whip and Pokra. If they would add 1 more (or perhaps I'm forgetting one), you could have one different melee attacker per lane. XD