eh, the age gaps get less noticable the older you get. Also 70 year old men, depending on lifestyle (and uh...other stuff), can be extremely fit and good looking still. If anything women sadly fade quicker.
Bianca's specific case makes it even more likely. Her life expenctancy is likely shortened by several years, bringing her close to him, and she will be seen by many potential partners as baggage with her disease. Maybe even Ioan himself, he might actually want somebody to care for him when he is 80, not the other way around.
That's the theory, obviously some of your points are correct: Ioan has extreme baggage with a hell ex-wife that has a vendetta against her and estranged children who probably are also already programmed to dislike her. If Bianca is in this for the fame (again, it really shouldnt be ruled out that this is at least a large factor) and all about living in the moment etc etc and she does come along a more famous man that is prepared to accept her illness she might bounce: it wouldnt even necessarly mean that she is fame hungry, you have to consider your options, and a younger man with much less painful baggage and the additional perk of being able to provide the same (or more) is simply the better option. The question is just if someone with her condition would get this easily someone like this, especially later on when her health becomes a bigger issue.
I personally do expect this relationship to end relatively soon (with that I mean anything between a few months and 5 years), the movie will probably be a key point. If it doesnt get made will she just accept it or try to date a man with more influence to do it? If it does get made, then what? Will she be less respectful of his wishes because she got what she wanted (again, speaking hypothetically here if that was her intenion) or perhaps drop him all together? But you can never really rule out anything, I certainly never expected him and Alice to last over 20 years lol
Also btw most men leave marriages only when there is perspective for a rebound soon, might be weak, but it's common.
Alice said the other day that the kids stay with her until they have a deal. Now whether this means she simply doesnt gives them away and Ioan doesnt want to force them and further the PA that way, but also doesnt want to wait forever in his little flat in LA for them to never come and instead uses the time to reconnect with family and friends in the UK. Or whether this means that this is an actual agreement between both parties for stability/clarity reasons is something we dont know. The former would work very badly against Alice actually. The latter wouldnt work against either (but would completely rule out a sole custody, which I'm sure he didnt want and couldnt have given that he has to earn the money)
I'm sure anything he does will be approved by his lawyer. He wanted 50-50 custody in december and when he filed for the RO he mentioned custody handovers in there too. I doubt that he suddenly changed his mind and doesnt want them at all (even if Alice claimed this the other day too, but we know her