From a political perspective, why would it even matter at all if Lux were to marry Jarvan in a political marriage? He will eventually also find out she's a mage, so I doubt a marriage would make Lux "immune" to scrutiny by the greater Demacian anti-magic masses. The elite noble would continue to scrutinize and harass Lux for being a mage even if she were married.
There is no lore, stop thinking, everything get retconned like 8 times a week.
The masses aren't really the ones who are anti-mage though. As we see in Sylas's story, at least people on the outskirts are perfectly fine with mages helping them.
It's mainly the Demacian nobles who want to maintain their power.
So if Jarvan were to marry Lux, it could lead to infighting among the nobility. And then they'd end up picking sides, likely with Jarvan-- who is rather more kindhearted and open-- being on the pro-mage side. It could even put a preemptive end to the rebellion Sylas is attempting.
Because Jarvan's a goddamn hero of the people and if he thinks Lux is down with the crown then you know damn well the masses will follow.
Jarvan uses mana so he has magic affinity; so maybe he can help lux control her powers and keep her safe
So she doesn't actually marry him right?
Cuz that would just be fucking weird.
