The SHE model is expensive but its actually surprisingly not that hard to find. I've been here a bit over a half a year and I found two during the first several months.
There are so many problems to casting a variable YF-19. To put aside the fact that non-model people will want a durable-sturdy-already-built variable YF-19, theres plenty of other problems besides that...
First, we need to find someone willing to find a transformation sequence that will work with a kit bashed Hasegawa. Even after all is done with the transformation, we need someone skilled that is willing to make the parts that is needed to make it variable/posable... which will be quite a lot. The entire back, rest of the arm, hands, rest of the head, rest of the shoulder, different feet, the crouch peice, and whatever else im forgetting. This is not even including the modifications needed to add joints to where its needed. So lets say we even get passed this part. We need to find someone to recast it for the rest of MW which will in turn be quite costly since there will be a lot of complex and small pieces. Even the cheapest recasts of a variable kit will in the ballpark of a hundred dollars... and thats dirt cheap. Look at the variable IHP VF-4 in the sale forum for example.
So basically in the end of it all... we're going to have people spending tons of hours and effort just to save a bit of money and enlarge the scale to 1/72. Sure, to people like me whos not expecting to do any of the work and plan to sit around until others are done with it, it totally seems worth it but to those working on it, I'm not too sure. Thats up to them to decide.
I'm a model person too and would LOVE to see this happen but unfortunately, after taking a good look at it, I doubt theres anyone willing to take on this job and wont mind not being able to profit a good amount for their work.
My take on this would be to take Pat S's custom YF-19 and have someone like Rohby recast the parts needed for the modication and for those who's willing to take apart their Yamato, have a slightly better and more posable YF-19. Problem with that is that might end up being a pretty penny as well.