Back in September 2013, we heard rumors about a new premium phone from Samsung with the name "Project F". They had planned a release in the second quarter of 1014. But now we know that they might launch it alongside with the Galaxy S5, under the name Galaxy F according to ET News.
The most reliable rumors say that the body of the Galaxy F will feature a metal body. It was originally developed in Europe but was later moved to Vietnam for mass production.
Older rumors believe it's also possible that the phone will feature a QHD display (2560 x 1600) and other premium components that set it in a league higher than the S series. Samsung has not confirmed anything of this so these are major speculations.
If this will be successful is hard to say, having in mind that Samsung already have many devices in the S series and other mid and low end phones. Many Samsung consumers say they enjoy the plastic around the phone, but others may prefer metal. Who knows, maybe this is Samsungs way to please both groups.