So will the new factions be allowed to fly with the old factions. Im guessing yes

Your making the assumption that there will be new factions.

A variety of reasons makes that unlikely, though I can certainly see the other side of the argument.

If you look at the previous leak, you can see that the back of the First Order dial seems to be black like an imperial one.

Scum, as a new faction, has dials with a green colored back. Maybe, that indicates, that FO and Resis are no new fractions.

I thought that the new symbols were new factions and doesnt it say on the box there are new factions eg the Empire is dead but there is the First Order.

I can see these being new factions even if in just name. However, that doesn't mean that similar alignments can't be used in "mixed factions," and that's not a new idea for this type of game. If anyone remembers WotC's attempt at this (if you forgot, sorry for reminding you), those were divided into Light and Dark. Something similar can be done with these very easily since they are past and future versions of each other.

Currently, I see the alignment issues as making a mountain out of an imaginary mole hill, and it will stay that way until we know something official.

Fo and resistance are new factions in name only

In gameplay and in fluff, they're carbon copies of rebellion and empire

Otherwise good luck reliving the movie with incompatible t70s and Falcon...

I don't see why scum is a faction that the other two couldn't hire (at a point cost price).
Mixed factions should have been a thing already IMO.

I could think on FFG introducing subfactions, and maybe some Subfaction Cards that are like permanent effects that affect ships of a particular subfaction. So a player would choose a subfaction along with their squadron.

I don't see why scum is a faction that the other two couldn't hire (at a point cost price).

Mixed factions should have been a thing already IMO.

If S&V were a neutral faction available to use for the Empire & Rebellion they would need to be balanced to work with both, that increases the difficulty of design and play-testing exponentially with each pilot and upgrade added (there's a number guys on the forums would can explain the math behind this). This would severely limit the design space for S&V. You probably would'd see pilot abilities like the ones Serissu, Xizor, and Torkil Mux have because of how they would interact with existing pilots. Imagine a tie swarm with Howlrunner & Serissu, or Jan Ors giving Kavil a 5 dice blaster turret attack.

But no one's stopping you from combining them in casual games as long as your friends are into it.