The fact my models don't have closing S-Foils would kill me

But isn't that just because we've not seen any subfaction only upgrades?

Yes... and no I suppose. There's cards that say Rebel only on them. So I guess to make things easier they named the Rebel Alliance/Resistance faction Rebel. Then they wrote the rules so that upgrades belong to the Primary faction, not a sub-faction. So per the rules there is no such thing as a subfaction upgrade. In fact you could argue that RAW, an upgrade that said Resistance only on it would actually belong to the Rebel faction.

So to fix that they'ed have to errata the rules, and that's something that should IMO at least be avoided if possible because it causes confusion.

The fact my models don't have closing S-Foils would kill me

There was a post here at one point where someone modded their X-Wing so the wings closed. There was detailed instructions for how to do it.