I'll write down some thoughts. First off, I think Sideshow wouldn't do something like "Cobra Commander Faceplate Head" as an exclusive...they seem to have lately geared away from that so that any exclusives would be just an item that most people could live without. Which I applaud since it makes the figures more accessible to everyone without putting too much bearing on a special item that is limited.
Here's some ideas
Cobra Commander: Black Cape with Red Inside. CC has been seen in the cartoon and comics sometimes wearing a cape. However, I can almost see a cape and a "Cobra cane" being regular accessories for him as well. Another idea is a Globe (like you have in your classroom) with a Cobra coiled around it...this item was seen in some of the comics mainly when CC first started Cobra. There could also be the MASS Device crystal.
Snake-Eyes: If they go with v1 (Commando style) I can see them adding an extra gun or a hook and rope (to pose him like the cover of Issue #21 "The Silent Issue"). If they go with v2 (knight visor ninja style)...a HUGE exclusive would be the inclusion of Timber like was mentioned before...but they could also go with something like some ninja stars or another ninja sword.
Duke: Jetpack is definitely a good idea, maybe alongside the American Flag on a flagpole. His helmet might be an idea as well as some additional guns. It's hard to tie Duke to much else...
Zartan: Multiple disguise faces that can attach on. Maybe even a "Cold Slither" guitar or something? Depending on the version design, you could also maybe give him a trenchcoat.
Dreadnoks: Grape soda...definitely. Or some cool Dreadnok logo "pleather" biker jackets.
Lady Jaye: If they give her spears, make the exclusive be the speargun. If they give her the speargun, make the exclusive be some extra spears.
Shipwreck: Polly as an exclusive for sure. Could also give him a life-jacket... or to go on a limb here, a different shirt and hat instead of the traditional white/light blue sailor stuff...give him the modern black wool shirt and beanie that he wears in the comics nowadays.
Baroness: Give her a long black coat or something like that, she's looked pretty slick in the comics with one on over her uniform... or perhaps just Destro's mask.
Destro: His mask by itself, or perhaps an ornate sword (based on the '88 version's sword). Maybe even a MARS briefcase with a removeable gun from the handle (like the Sigma Six figure).
It's tough thinking of some because most of the accessories I think of are the ones that came straight with them and should be made with them NO MATTER WHAT (like Snake Eyes' sword, Scarlett's crossbow, Flint's shotgun, etc.).
Perhaps Sideshow could also do a "Pet pack" (much like SW's creature pack) and include Timber, Polly, Freedom, and Order to name a few if their respected human "partner" has been released.
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