Hello Varun,
Linked universes are back in BI 4.2, you can have some more info about them in the BI 4.2 what's new (SAP BusinessObjects BI4.2 What's New L2) and more detailed information will follow shortly.
About support of UNVs, as of now there is no planned date or for descoping them: as long as BI4 is supported they are going to stay (which means *at least* until 2020, but this date will move forward if we release new version which support them).
Now this is not necessarily a good reason to continue to develop new UNV as, even if they are supported, all new functionality (and sometime new connectivity) is going to be added to the UNX format.
Hope that it helps
Regards
PPaolo