Now that both The Flash and Superman are appearing in both the movie and TV universes (played by different actors; movies and TV are separate universes), it’s possible WB may have relaxed their rules surrounding the sharing of characters. It’s actually a great route to go as WB can take advantage of their popular characters across all forms of media, than say Marvel, which has one big shared universe (but no mention of the TV characters is ever made in the movies).
Regarding Batman, Bleeding Cool is stating that Fox currently has the TV rights, which is tied up with Gotham, but Fox may share the rights for a fee.
Constantine with Matt Ryan may get revived as part of the CW’s supernatural Friday as The Vampire Diaries is ending, and The CW may want to go with Constantine to fill the horror gap.
Batwoman is said to be appearing in Supergirl with Kathy/Kate Kane being Maggie Sawyer’s ex, whose adventures as Batwoman occasionally take her to National City.
Oracle Barbara Gordon is also said to be coming to Supergirl (though apparently not as Batgirl) where she befriends Kara, and the Oracle/Batwoman relationship/plot is said to resemble Birds of Prey.
The Flash‘s John Wesley Shipp is said to be another cross-series regular, probably as Jay Garrick (similar deal to Wentworth Miller and John Barrowman).
It’s possible some of these announcements may be made this week at Comic-Con.