The title pretty much said it all but I'll expand a bit more- the ability to see possibilities and how those possibilities would make a domino affect of change is absolutely overwhelming me lately.
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TL;DR I can't hold any vision of the future for anything longer than a few days.
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How the heck do you guys get out of this kind of rut? I can't be the only one who struggles with this, right. So how do you do it? How do I stabilize my writing process? What helps you to find stability and endurance??
Not sure if that helps you directly in any ways but I try to explain how similar things work for me.
I believe this constantly changing view about the world around us and our thoughts is pretty much okay - otherwise we'd be some other type

That's perfectly okay and we don't have to fight against who we are. Instead, we might want to learn how to take advantage of that. I can relate well to what you described but I haven't had exactly the same concerns by myself as you do. Don't know why's that - maybe because I'm always been quite Fi-heavy which somewhat grounds/balances those possibilities because it helps to choose paths you feel the best about?
I take similar situations something like this: using somewhat "fatalist / believe in the faith" attitude. It means actually that like you, I can't predict too where all the possibilities we might have in our heads, could lead to. Thus can't decide which one of them would be the best.
So what do I do then? Usually I just let the "game" play out without thinking much about the future possibilities and then just quickly adapt to the changes if I have to. Remember, this is one of our type's strengths right?

We ENFPs after all aren't plan people, we're more like explorers or wanderers - so why not take advantage of that conciously.
Can't explain why's that working and sometimes it feels even a bit unbelievable but I've had enough proof in my lifetime that I can rely on this approach

Usually right things tend to happen exactly in right time and right place when I need them the most. It feels like when there's an issue, there's always solution right ahead and quite quickly it makes the ends meet.
On the other hand, it's quite logical after all - if you don't have any plan written to the stones (our type could even fail to do so), it's hard to miss the optimal choices if you meet them as you're not just bypassing them because you didn't have a plan which said you have to go anywhere else, right?
Similar seems to work for writing too - if I have to write, I'm constantly changing the way my writing rolls out. When reaching to some decision point, I scan all the possibilities which fork at that point and see how I FEEL about any of those RIGHT NOW. Then rinse and repeat

I never have full story fixed in my mind in linear way before starting to write it.
Of course, the story could be different every time I'd repeat the same approach but there's nothing wrong with that. Btw I had a lot of trouble at school time when I had to write essays because they teached to think about them in linear fashion. Once I discovered later in adulthood that writing is not a linear process but expanding ideas, there's barely ever a trouble with that.