There's been a lot of fan speculation that the Fourth Doctor and the Second Romana's relationship was more than just a platonic one. Some fans also think the Fifth Doctor and peri had something going
In Micheal Moorcock's Oswald Bastable trilogy there are a couple of timelines where WW1 never broke out. I think in the third book "The Steel Tsar" it was something to do with no German unification and prussia being a major power instead.