lol. It begins agaaaaaaaaiiin.
I still stand by that ZUN was basically saying, in answer to the question, "What is the relationship between Maribel and Yukari?", his answer basically meant "It's the same as Lafcadio's relationship to Koizumi." Of course, the most important thing to most people would be the whole "Lafcadio Hearn moved to Japan and changed his name to Koizumi Yakumo" so "Maribel Hearn moved to Gensokyo and changed her name to Yukari Yakumo" (but with time travel shenanigans!) thing, but there's a ton of other analogues too, like Yukari being dubbed a youkai expert just like Koizumi and... well, anyways, all the POSSIBLE relevant evidences I could find are at the wiki. There's just so many things strewn about which could be there because Maribel eventually "grew up" to become Yukari.
Of course, it could all be just coincidences and/or misinterpretations. *shrug* I'm of the firm belief they aren't and that the vast majority of them ZUN put in on purpose due to Mary and Yukari's true relationship, but obviously peoples' mileage may vary.
(The Hakurei Shrine god is Mima. Everyone knows that!

....although in all seriousness she did canonically try to become its god for a brief time. She ended up dropping it but hey, maybe she gave it another shot later!)
It's Christmas I'll bite.
My personal opinion is no. The whole 'Yukari is Maribel when sleeping' theory was jossed in 7.5 and 9.5; as well as 13.5; where Yukari is clearly awake during the daytime. All of these games are canon; and I think we'd have heard of Maribel going into comas randomly if she was doing so whebever Yukari was awake during the day.
The more likely (IMHO. ...although IMHO "almost certain" would reflect my own personal beliefs more) is that Maribel grew up to become Yukari after time travelling to the past. The "Maribel is Yukari while sleeping and vice-versa" idea just has too many contradictions, as you've pointed out, and doesn't really match the Lafcadio Hearn Koizumi Yukamo relationship, either, nor does it have as many circumstantial evidences such as the ("probably") fact that Yukari isn't Yukari's actual name.