Thanks achow for your answer,
The others were saying if Lightning Network was possible without SegWit and it is true? or SegWit was becoming a responsibility for Lightning Network.
Lightning is certainly possible without segwit, it is just a lot harder to implement and more complex. Segwit makes lightning easier to implement and less susceptible to failure.
Why bitcoin core has opted the complex softfork rather than be implemented into hardfork with more simply and cleaner.
As I said earlier, hard forks are neither simple nor clean. Even implementing segwit as a hard fork would not be simple nor cleaner. Either you break every single unconfirmed transaction, or you go through the pain of a hard fork for basically no reason as the things that would require hard forking can and are already done in a way to allow soft forks.
adoption takes time, why?
Because people are testing the software and upgrading custom software. Also a lot of pools seem to not support segwit for some reason.
when we can expect >90%?
We can't predict the future, no one knows.