I'm not sure. I hate to say never, because who knows what life will bring and maybe a breed I love but don't think fits my lifestyle now might later on. But right now, breeds I love that I don't foresee actually owning anytime in the near future or possibly ever depending on circumstance are:
Leonberger: Major love for them. Just too big for what I currently want in a dog. If I ever have one, I'll have to have a larger house so I don't feel overcrowded by a large dog (Ripley verges on too large/in my face in our average sized home).
Dalmatian: Dals have been a long time favourite of mine. I love them so, so much. I actually can see myself with one eventually, but right now I don't want anymore smooth coated dogs and I wouldn't want one along with a Doberman for some reason lol. Not sure why, just doesn't seem to go.
Siberian Husky: I tried to convince myself that I could be a good home for one, but I really don't think I'd enjoy one all that much. I'd probably be pretty frustrated. But I do love them. They are one that I can say I'll never have but I love. Same with Alaskan Malamutes. I like them just as much.
Border Collie: I really like the breed and used to want one, but I like a very specific type of Border Collie personality. I think I could like the right one, but right now I love Aussies more and if I ever get a herding breed that's not an Aussie, it'll probably be a Koolie before a Border Collie just because Koolies seem a little more silly and they just in general appeal to me a bit more.
Dobermans: Yes, I know I've had three (and a foster), but I'm still putting them on my list haha. I love them and they'll always have a special place, but it just seems too difficult to find the type of Doberman I like and would want. There is a big part of me that wants another black girl, but I want a certain personality type that seems hard to find. Plus, the wimpyness about going to the bathroom in the cold gets old haha.
Belgian Groenendael/Tervuren: I love them and have wanted one since about 2005, but I just don't know if I could be a Belgian person. Maybe someday, but not right now. For as dog experienced as I am, Belgians in general seem to be rather quirky, and I wouldn't want to mess one up accidentally.
Rhodesian Ridgeback: I love them and loved the ones I knew, but they're just not for me as far as any degree of permanent living would go.
As far as breeds I have to have, that's a tough one! I own the two breeds I've loved my entire life (Aussies and Tollers) and don't have a strong desire to stray away at the moment. I'd like to be more involved in Aussies in particular which will probably leave less time/energy/money to own other breeds. I'd say Koolies used to be on that list, but now that I know one (who to be honest is not what I expected lol), I don't feel like I have to have one anymore. I still love them a lot, and would definitely still seek one out from specific lines, but I'm glad I got the particular Aussie I did (whom ironically is everything I thought a Koolie would be). So yeah, at this point in time, the only breeds I have to have and daydream about constantly are more Aussies and Tollers.