The average world purchase price for a phone is around US$350. This is over FIVE times that.
The G Fold is almost certainly going to be even more expensive.
And people aren't going to be upgrading "just 'cause" every year. This is going to be an impulse purchase for many of the small group who can afford one.
So yeah, I would be reevaluating market demand right now.
Samsung has reportedly confirmed that it is ready with the tri-fold and can put it into production. However, the demand for it is being currently studied and it may be a while before we see the production model.