Abelard won’t ever date, let alone marry, somebody with helot origins.
Unless the author changed the ro’s around…again. 
I feel, in general, that your Joan story might work better if the mc could be one of the more impoverished, but technically free yeoman of the Rim, instead of a slave.
Non-radicals won’t really free the helots, the economy depends too much on both their blood and involuntary labour.
Best they might manage is either sefdom with only theoretical “rights” or if they are very, very progressive some form of sharecropping with debt bondage. But that latter, in particular, would require blood to become much less central to the economy and the switch to a fully monetary economy where a person’s economic value is measured purely in money and not blood or aether.
Right now helots are forbidden from even handling money it seems.
Now we know Havenstone deliberately limited the mc’s background to the two extremes of the fictional society, nobles (even if impoverished) and slaves, More character archetypes would naturally have been possible if the mc had been allowed to have a yeoman, urban poor or merchant class/caste background.
As it is we will probably see those reflected in other rebellions and factions that the mc cannot (directly) lead themselves. Cabel, for example, seems to represent a Shayardene homelander yeoman faction and I’m sure at some point we will see some factions with merchant class origins popping up too.
Now, that said, If I really were determined to turn a helot into a “noble” on their “merits” and not by some bullshit “divine right” or “sacred bloodline”, the best avenue would be to go cosmopolitan and exploit and expand being made a Wiendish clan leader for all it is worth.
Still that is not quite a king or emperor on its own, but with some deft management and luck it may be possible to parley clan leadership into becoming the high king of Wiendrj.
As, like @P_Tigras said, you may well need to kill half the nobles/clan leadership for them to accept the mc and their new clan as legitimate and that leaves a lot of room to make sure that the new clans or the new clan leadership that will replace them start out as your loyalists, who can then elect the mc, former helot or no, high King.
To rise further from that point a cosmopolitan mc would need to play Horion, or at least the leaguers in Shayard and probably some other factions in the other provinces like a fiddle, subvert some of their assumptions and then divide and conquer.
The easiest way to do this would be to both go along with the idea of a Koinon but also transform it a bit from Horion’s vision, particularly when it comes to Shayardene leadership. This would almost certainly require a much weaker Shayard than what Horion is banking on. Which means the mc would need to exploit the cultural divisions in his (former) homeland for all that they are worth to split what is now Shayard into at least three pieces and have its northern, anglo-saxon, southern, french-esque and the Reach separate into their own states.
Along with, again, some luck and deft politicking that would open up the possibility to make the Koinon more like the Holy Roman empire, only without the holy and the roman, and introduce an elective emperorship that is not tied to Shayard but, theoretically, open to all member heads of state.
From there the mc, as a high-king should be able to engineer the first election in a way that allows them as the original rebel, who started everything to become the nominal “emperor” of the Koinon.
That is practically the only way I can see to turn a former Shayardene helot into an emperor on their own merits and without needing to forge a bloodline or lean heavily into bullshit divine right doctrines.
Now, compared to my more traditional, Mao-escque vision for my helot mc I do not think the compromises necessary to make such a route a success would be worth it as the necessity to play nice with at least some of the noble factions would greatly limit what reforms you can do and would probably end in half-measures such as the aforementioned replacing the helotry with serfs or at the very best sharecroppers.
While the mc shouldn’t have to repudiate their helot origins in this path there would still be an unfortunate necessity to adopt some more disturbing “noble” mannerisms, clothing and decadence disguised as “honour”. 