Is there an easy way to know whether a given BIP has been merged or whether its still in work?
Yes it's easy, just refer to Bitcoin GitHub Repository's doc directory.
Link:
https://github.com/bitcoin/bitcoin/blob/master/doc/bips.mdFor the dates, most of the entries in the link above have notes on which version it's implemented, do a quick research of when those specific versions are released.
These are BIPs implemented in bitcoin core. Its not necessary that you will find all the BIPs in this list.