A replacement for B757's expected in service from 2025.
There is????? Do tell, mainly as by then the youngest B757 will be about 25 years old.
The A321 can do the majority of the B757's routes for much less cost, the B737-800/900/ERs even more so, at the upper end the B787-8 is a much more capable aeroplane. Hence there's not much of a gap to squeeze in the middle, only United and Icelandair will be flying B757s across the pond regularly in the next few years. Delta withdrew (most if not all of them are now US domestic / Americas) and American are currently in the process of doing so. There's a few randoms like Aer Lingus using some young B757s but there's not enough of a market for an all new aircraft, far from it.