Planeswalkers are always eyecatching, so here’s the recently spoiled Narset:
Of course, most people will first think WU Control, but no. You need to think this through.
First, Narset’s ability to draw cards isn’t that good. You’ll get around three cards for five activations. Do you really want to have such a slow card drawer in your deck, when you have a limited number of spots for card drawing in your deck. Do you really want to run this when you have so many faster choices? There’s Treasure Cruise, Dig Through Time, Divination and Jace’s Ingenuity, at least. Narset would occupy a pretty awkward spot here. You need those removal spells and counters fast. You can’t actually wait for several turns to get what you need.
The second ability is particularly awkward. Sure, you can rebound card draw spells, but again, you have limited space for such spells in your deck and if you play Narset, those spots are even more limited. Then, if you are white-blue, your answers are often pretty narrow. Think about the white answers (that are instants or sorceries):
With the exception of End Hostilities, these are quite situational. And if you have a sweeper on the rebound, your opponent simply want commit any creatures on the battlefield, or he or she will simply use dash on that turn. Of course, if your opponent doesn’t have dash creatures, you’ll gain one complete turn of piece from creatures (not against burn, though). Counterspells don’t do anything during your upkeep. The spot removal has all sorts of clauses, which limit their usefulness and some of them can’t even be rebounded.
All in all, Narset would be quite awkward in a control deck. This doesn’t mean she’s useless, however. Her place is actually (quite ironically) in a Jeskai Burn deck.
Not sure about the Outpost Sieges. Its a great card, but Dig Through Time could be rebounded. Also, in some metas Monastery Siege could be better. Maybe some mix of those and Digs could be best to feed your graveyard and gain full benefit from it.