Yep, it'll absolutely positively be released before 2025, and will include a free pink pony and/or unicorn in every box.
Seriously, though, this question gets asked at least once a week, and the answer is always the same: the Raspberry Pi Foundation has not announced any details of a Pi 4, and they generally do not pre-announce things, and asking for hints just annoys them. The tea leaves say that most of the changes that folks would want to see (USB3, more RAM, etc.) will require building an entirely new SoC (the chip that provides nearly all the functionality of the Pi: CPU, GPU, etc), and that task is neither cheap nor quick, so don't hold your breath.
What we do know: the CM3 just got released, and the Foundation is on record that a Pi 3A (effectively a Pi A+ with the Pi 3B's SoC) will be along "soon" after the CM3 (for unspecified values of "soon"). Anything beyond that is merely speculation.
The Pi 3B and Pi Zero are remarkable little machines - get one, or several, and enjoy making them do neat things now, and be happily surprised when the Pi 4 arrives someday. They are known to be i/o bandwidth limited, but can do some really interesting things.
Last edited by CarlRJ
on Thu Jan 19, 2017 7:41 pm, edited 4 times in total.