If you look closely at the preview picture for the Mist Hunter, you may notice something interesting. It has 6 (!) rules reference cards, including this one:
Dual [...]
Dual upgrade [...]
they do not h[...]
Furthermore, the top left upgrades read as follows:
Adapt[...]
D[...]
Since "D" can't start "Scum and Villany only" or "Small ship only" or "G-1A Starfighter Only", it's probably the start of "Dual" or "Dual upgrade".
I'm going to guess that the Dual Upgrade reference card starts like so:
Dual [upgrades]
Dual upgrade[s are unique in that]
they do not h[ave (a squad point cost?) (a type icon?) (a back?)]
It's probably not the "two type icons" mechanic that Emperor Palpatine has, as there was no mention of Dual Upgrades in his preview article and I think it is self-explanitory enough not to warrant a rules reference. Also his text box doesn't start with "D".
Here's some speculation:
• Dual upgrades have two faces. They can be flipped from one face to another, perhaps at the start of the activation phase, or whenever the carrier executes a certain class of maneuver. Adaptation is a two-faced upgrade with each face being useful in a particular situation. You flip it to adapt, hence the name.
• Dual upgrades are a pair of two upgrades with the same name, but a different text box, hence the inclusion of two copies. You can swap one version for another under certain circumstances. The Adaptations are each good in a particular situation, so by swapping you can adapt, hence the name.
• Dual upgrades are a pair of two upgrades that you equip to two ships in a squad and they and/or the carrier ships are linked (hence the two copies). For example:
Best Buddies
While there is exactly 1 other friendly ship equipped with Best Buddies in play, roll an additional attack die when attacking.
Type: Elite
Squad point cost: whatever
This probably wouldn't warrant a reference card.
• Dual upgrades have two different type icons and can be equipped as either type. This could be communicated by having both icons in the corner with an "or" between them, which wouldn't need a reference card, so I don't think it's likely.
• Dual upgrades are upgrades that need so much text they can't fit on a single card. Two linked cards function as a single card, basically expanding the text box.
In the past, Fantasy Flight has used rules reference cards to compress text. For example, instead of writing out the rules ofr how a Seismic Charges works on the card, they used "detonate" and "deploy" keywords and wrote the text on a rules reference card. I doubt they'd resort to this.
Also, in a pinch, they can just print pilot card-sized upgrade cards.
Finally, if this was true, I'd expect them to trim the art box on the second copy to make room and Adapt[...] clearly has art on both cards.
Any other thoughts on what Dual Upgrades could be?
Bonus speculation: Another of the Mist Hunter's rules reference cards reads "This card [unreabable two letters][...] an ion token [...]".
It's not the card for ion tokens, as none of the Mist Hunter pack's cards can give those out. It's also not the Tractor Beam card, unless tractor beams need two reference cards. There is another card clearly titled "Tractor Beam Token". Is it an updated decloak card outlining how decloaking interacts with ion tokens? A second tractor beam card detailing how ion tokens and tractor beam tokens interact? A card detialing a new mechanic from "Elec[...] Ba[...]" and how it interacts with ion tokens? Discuss.