It is going to heavily depend on how much of a reform Swain attempts to invoke. Obviously he has Darius in his back pocket, and it seems to me that Darius's vision of what Noxus should be is pretty close to what Riven's ideal is, so it could be that Swain could gain Riven as a major ally.
However, Swain also has Leblanc as a major ally, and she is connected with the Black Rose. According to Leblanc's lore, having the aristocrats in charge is ideal for that group, and this would be counter to Darius's ideal Noxus, and by extension probably Riven's hope for Noxus.
Right now Swain has a nice balance between the two. Outwardly he is re-militarizing the Noxus leadership, while it seems inwardly he is ceding power to the Black Rose. Further more, Leblanc has a problem with General Du Couteau because of his loyalty to Darkwill. And now that Du Couteau has disappeared Katarina and Cassiopia are none-to-pleased and are going to be actively working on this mysterious disappearance of their dad.
So Swain is going to have a choice. Sooner or later, Katarina and Cassiopia are going to force him (either by ultimatum or just circumstance) to either give up Leblanc and the Black Rose for their involvement in the disappearance of the General (making himself the enemy of a very powerful shadow group), or he will protect her and there by potentially alienate Darius, Riven, the Du Couteau family, and piss off Talon.
I think Swain is going to protect the Black Rose since he was formerly affiliated with them. Katarina, as head of the Du Couteau house, would then form her own group, the Crimson Elite (because for some reason I think the Du Couteau-line is mostly red heads; hence "Crimson") and then go on a war path to destroy Swain, Leblanc, and the Black Rose.
Or, most likely, this is a load of fan fiction. But I think it would be sweet if it was real.
Swain was not involved with the invasion of Ionia. The same invasion that alienated both Riven and Sivir.