I hate playing fantasy booker, but here's something that I think would work wonders for Sheamus, as well as revitalize a veteran who has been floundering on Smackdown since getting transferred there. It's a feud I'd definitely be able to get into, and it would be a lot of fun to watch:
Last night, we've seen a side of Sheamus that they really didn't delve into during his ECW run. Sheamus, in addition to having an awesome unique look, and a really good moveset with a brutal finisher (The Irish Curse), as well as having a backstory I really like, with him being the descendant of Celtic Warriors, decimated Jamie Noble. The way he destroyed him showed that he has no remorse, and that he's focused on destroying whoever is in his path. Now, it's been alluded to that Sheamus is very proud of his Irish heritage. What they should do is eventually lead us to a match where he takes on Chavo (who has been slowly teasing a face turn), and Hornswoggle gets involved, helping Sheamus win.
Sheamus doesn't take kindly to this. He likes taking care of his opponents himself, and he especially doesn't like the fact that he won thanks to Hornswoggle shenanigans. Sheamus proceeds to destroy Hornswoggle, much like he did to Noble. Sheamus defends himself following the brutal attack, stating that he's the descendant of Celtic Warriors, and that he's proud of his Irish heritage. What doesn't make him proud is the stereotype of leprechauns, and always getting drunk, and the usual Irish stereotypes that we see that are portrayed. He sees Hornswoggle as a prime example of what sets back the Irish, and he beat him up to prove a point.
This takes Finlay out of the midcard purgatory that he's been in on the Smackdown brand. Hornswoggle is his son, and he has to avenge him. This leads to a bitter feud between the two that could most definitely be awesome. Finlay and Sheamus would have some great brawls if given the opportunity. It would also give Sheamus a way to get over on Raw, while the rest of the midcard guys that they're starting to push (i.e. Bourne, Kofi) are protected by doing their own thing.
Triple H stated in interviews that Sheamus has the right attitude. He shows up to shows that he's not even scheduled to work. He trains with Triple H on the road, and he's always wanting to go above and beyond. Sheamus is going to be huge, and I think he's got a great shot to be a World Champion in at least three years.