When Warner Bros. announced that the TV series's wouldn't connect with the movies a lot of people were disappointed. I for one wasn't because it gives the writers freedom to use the material they want. If the TV series were connected to the movies we probably wouldn't be seeing all the characters we are now on Arrow and Flash. So I like the way Warner Bros. are handling movies and TV.
However, one thing DC Comics is known for is their multiverse. Like Earth One and Two, which have the same characters but with re-imagined stories and changes to origins. Writer/Executive Producer Geoff John's even admitted thats what the individual TV universes would be like. Even the movies could be involved with this. So the movies could be in Earth One, Arrow/Flash in Earth Two and Constantine in Earth Three. As for [Gotham](series:1127075) I don't see why that needs to be part of any of the universes because its not the type of show that links to the present. I wouldn't get your hopes up with all these universes to collide some day but who knows, maybe Warner Bros. were planning this from the start. Arrow/[The Flash](series:1068303) already have the bigger universe at the moment, but in the next few years were gonna see the movies build a Justice League, and maybe the Constantine series will work towards a mini universe of its own. After the Dr. Fate easter egg in the pilot, my theory is that they'll try and create the Justice League Dark.
I haven't read the Crisis on Infinite Earths storyline yet but its definitely on my list to do so. In this comic series the Multiverse faced an epic threat by the enemy known as the Anti-Monitor. This was a major turning point in the DC universe as countless parallel universes were destroyed.
Of course this would be a tricky and complex story to pull off but if Warner Bros. did announce this I would not only be surprised but mega excited. Though again as much as some of us would like to see this, don't get your hopes up. Especially with some of the networks the TV series are on. As awesome as a movie would be, Warner Bros. may still want to keep the TV series and movies separate. But then they could still do this as a mini-series for all the TV shows. Would be a shame if the whole Multiverse couldn't be involved, but there are still plenty of other mega events that the movies could use if the TV series used Crisis on Infinite Earths. If this did happen it could mean the end of some of the universes so I wouldn't expect to see this for quite some time.
Marvel have their Infinity War coming soon, and for DC to have a Crisis event that would just top everything.