Sure, the UVs are different for some parts, but not for 90% of the model by the looks of it. Plus, not only that, but the majority of the skins are extremely simple and, barring the Onionhead and camo ones, would need no additional alterations other than matching the colour of the new elements to the base colour of the rest of the ship. Updating the tactical and vibrant packs would probably take no longer than it takes to paint bucket the correct colour and click save... The £10 Chrome and Wireframe models would also be extremely simple by the looks of it.
I do agree that two separate maps would be required, but the work involved in porting over the Mk. III skins to the IV should be minimal at best IMO and I think it'd be pretty harsh to expect existing owners to pay full price again, particularly for the £10 skins. The Mk. IV is a bit of an oddity too, being itself a limited edition and thus I'm not sure how many paints they might do for it. Another reason why it makes sense to me to update the existing skins for such little effort. The ship should, IMO, also be a significant upgrade from the III and I'd imagine would replace the III for most people, in doing so rendering their expensive skins obsolete. Of course FD may just duplicate the existing skins and then charge full price for them. Some will moan, some won't; the usual story

. However, knowing that that move is unlikely to go down well, they may choose instead to not update them at all, which would be a shame and leave some of us with pricey redundant skins (assuming of course that the IV's
generally speaking the much better ship and if it's not, then what's the point of it as most of the experienced players it's intended for will not give it a second thought at this stage of the game).
I can understand that FD don't want to set a precedent of 'Variant skins are a single purchase,' but I think they need to be pretty careful, particularly regarding the premium £10 ones. I know I want to see my chrome skin on the Mk. IV, but I'd be very hacked off if they sold it again separately for £10. I'd also be somewhat annoyed if they simply didn't update it for the Mk. IV at all; the ship was meant to be a gesture of gratitude for buying Season 1, to then to not allow us to use our expensive paints with it just doesn't make much sense, especially given the ease in which they could be added. Don't put us in the position where we want to pilot the IV, but don't want to because we can't use our favourite skins (which let's face it, we paid way over the odds for). That would just be really frustrating and so easily avoided.
Anyway, I'll leave it at that! Hopefully they'll come up with a decent solution

.
(Speaking of chrome models; when checking the Cobra paints just now, I noticed that FD have added an £8 Vulture one to the store, not that that one interests me personally but I don't remember it being announced).