I honestly don't see where room on the sprues will even be a problem, unless WA is going to be using going back to the smaller-sized sprues like those from their earlier sets or something: the bits that tend to take up room on the sprues are weapons - especially any variety of two-handed weapons and/or heavy weapons - and accessories like backpacks... since the zombies set appears to be including neither weapons nor accessories, and zombie arms do not seem destined to take up very much space nor deman much room, there's room to spare for most,if not all, of the head variety in the preview image.
For comparison, full-sized sprue sets like the Cannon Fodder II set had room for four different head types for five different bodies (cap, helmet, gas mask, shaved convict head), with plenty of extras, up to almost 40 heads on the frame, plus backpacks, heavy weapons, almost twice as many rifle arms as needed for the bodies involved, a couple pistols, several off-hand arms, and miscellaneous accessories including a grappling hook and knives.
Each of the full-frame WWI sets for French, Germans, British, and Russians has 5-7 bodies, and an avergage of around 30 yeads each with different styles of caps, helmets, and gas masks - the Russian frame has over 45 heads (the Germans had the lowest number - 24 heads - but include lots of entrnching tools, stick grenades, gas mask bags, and other extras to round out the frames with....) And that's in addition to plenty of rifles, machine guns, pistols, and other bits to work with. Most of these sets have six bodies per frame, but that Russian frame managed to fit seven. (The British set were the "losers" on the number of bodies with only five bodies, but made up for it with a great variety of heads, plus a wealth of entrenching tools, gas mask bags, packs, and other gear....)
For the zombies, we've been previewed six bodies, and six each of 14 head types, with a modest selection of arms:
(That's really not that many medium- or large-sized zombie bitz!)
Naturally, that preview image should not be taken as a promise that all those bits will make it onto the final frame, of course: WA can and does trim out the fat when fitting things onto their frames for final produciton.
BUT heads and weaponless arms take up relatively little room on these frams compared to, say, weapons, and without weapons and gear, it's not looking like it would be hard to fit most of those heads on a full frame with the bodies and arms - the ~84 zombie heads in this preview image is only double the number of heads from the Russians set - easily do-able.
Sure, I might be missing something in regards to the manufacturing process that might limit what could be put on a full-sized frame, but at a glance at a frame of the WWI Russians, the zombies - with one fewer zombie body than on the Russians and only about twice as many heads with none of the weapons that come with the Russians (there were plenty of spare rifles for those Russians!), it looks like it might even be easily do-able to fit all of the previewed bits on one full sprue. And it's not like the Werewolves, which are on a half-sized sprue: there's really not a lot more you could add to a werewolf set of the sort WA went with, even if you wanted to, unless you were to fill the frame out with regular wolves or something.
(WA doesn't seem to be doing a lot of half-frame sets these days, but I don't see any way to fill more than a half-frame of werewolves of this sort with alternate heads, arms, and gear!)
Looks to me like the room is there, they should use it, and what has been previewed looks to me like a fine mix of popular and eclectic options!
(They managed to fit a LOT of stuff on that full-sized frame of Russians!)
IF something needs to be cut from the bitz list in that preview image, I can't imagine it would need to be very much.
And with that in mind, I'm surprised nobody nominated the cowboy heads for deletion - I like them and hope they make the final cut (I'll be surprised and disappointed if they don'tl), but they seem to be the oddest man out of the preview: I don'tknow of any wargames demanding a lot of undead cowboys (maybe "Dead Man's Hand" and the occasional RPG like "Deadlands"), while fantasy and zombie-apocalypse games are surely the biggest markets, Silver Bayonet (yeah, that was the game I was trying to think of) can surely make use of those black-powder era heads, and the newly-realeased Wargames Atlantic product "The Last War" (using Forbidden Psalm rules) is only one of the Weird World War games that can make use of of the moderns. They're cool, but odd, and maybe the onesthat might get the least use! No, the zombie cowboys, Napoleonics, and tricorn guys are the oddest men out in the preview image within Wargames Atlantic's current public catalog, and the cowboys in particular are a bit niche for current wargames in general, but I think they're cool options for the set, and see no reason to think much, if anything, would need to be cut for a full-size frame of zombies....
Unless we have reason to believe WA's aiming at a smaller frame size, or plans to add zombie weapons or corpse-bits to gnaw on or something, I don't see any reason to worry about them running out of room badly enough to just give up on all the modern heads or whatever. And, I might be missing something from the communications - I'm not on Facebook, for example. Did Wargames Atlantic say somewhere that they would have to cut something, or did they give any indication this wouldn't be a full-sized sprue?