When it comes to some of the projects in development (Constantine, Preacher, Sandman, Y the Last Man), I can see where it would be slightly tough to link them into the bigger universe. And I don't think they have to be. But with Arrow, Batman vs. Superman/World's Finest (crosses fingers), Flash, Gotham, Hourman and Justice League, it would be helpful if they have some link through the different time periods. But it doesn't have to be thrown in your face strongly to the point it is annoying.
"Batman, remember when you grew up in Gotham and became friends with Selina Kyle while periodically running into Commissioner Gordon when he was a police sergeant and he coached you on being a better citizen?"
"Uhhhh - yes I do, Superman. Why do you ask?"
"I just wanted to point that out. No reason."
i think all the show like Arrow, flash, Gotham, and Constantine can still connect. lets say season 3 of Arrow we see metropolis before the events of MOS and hear about a myth in Gotham. in the season 4 finale of Arrow see the events of MOS which ties them together. same can go for Flash but since the show doesn't come out until fall i wait to see were it can go. For Gotham it can be sit 30 years before the events of MOS hell they can have Ben Affleck Batman talking to someone about his childhood and that's were the show starts. don't know about Constantine it could connect to that Justice League Dark movie De Toro wants to make.