You are not losing anything (of value*) if the Cobra MK IV becomes available for everyone.
*Except for whatever dubious emotional value one may have for that exclusivity, which I would roughly translate as "I have a thing that you can't have, loser".
But arguably it does have a value - it was part of an (at the time) expensive upgrade.
And it doesn't matter if it's a digital or a physical reward.
It doesn't matter either if a lot of us wouldn't care if everyone had access to it.
It's simple really. You can't advertise and sell something as an exclusive, then make it ... not exclusive.
There are consumer protection laws to prevent this.
The fact is that existing players were encouraged to purchase Horizons early with the incentive that the Cobra was an exclusive in-game ship.
So that's it - it was sold as part of that limited-time package on the store, and the exclusivity is legally binding. And I hate to say it, but because it was advertised as an exclusive part of a package, it may also mean that it can't show up on PS4 or future platforms either. (they come with Horizons so no chance to sell the pre-order package ... but I'm no legal expert)
FD painted the Mk IV into a corner and there's nothing else to discuss really.
Apart from all the angst it has caused, and will continue to cause, it was also a really daft idea to restrict the availability of a ship that you then might want to sell cosmetic items for. Hopefully for that reason alone they won't do this again!