What is the background? why is it happening? and what are the potential implications?
It's about compatibility. A fork occurs when nodes disagree on what blocks are valid.
A "hard" fork will occur when nodes start using software that now considers blocks valid that are considered invalid by current node software. If most nodes switch to the new software then old nodes will left behind.
A "soft" fork will occur when nodes start using software that changes functionality without the old software considering the new functionality to be invalid. Old nodes continue to function, but they are oblivious to the new functionality.
The segwit soft fork is achieved by hiding its functionality in an "anyone-can-spend" type of transaction.