But isn't that to premature to say that it won't do that since dark energy is not fully known yet?
Yes, it is. That's why the theory is sort of put on the back burner, as it were. It's not gone, and there are still proponents of it, but it requires more complexity to explain, and Occam's Razor would indicate that it's not the case.
For one thing, Dark Energy would have to have the property of pushing things apart, faster and faster, until something makes it change and begins pulling things together again. This would seem to indicate two flavors of Dark Energy, one that pushes things apart and one that pushes things together. OR that gravity, which seems to be losing against Dark Energy now, will wipe the sweat from it's brow, get back in the fight and deliver an unexpected knock-out blow.