I'm not totally in favour of connecting the universes but I'll be damned if they do not aknowledge the greater DCverse...I mean cmon, silly Smallville embargos should be over! Don't show the big guns if you really don't want to (though I'd still like Wayne to appear (needn't be in costume)) but at least hint at supernatural events in Metropolis (or Smallville) and a vigilante in Gotham...
That said...It'd be cool if the Arrowverse worked towards a N52 (don't get me wrong I mostly despise the reboot) JLA (or however they're calling them now)...what I mean is an anti-JL... ARGUS is already established, so they could hire Ollie, Barry, Sarah (or whoever will be the Canary), Vibe, Question (wishful thinking?) to take down this supernatural troubelmakers (an episod with that arc could end with them realizing that the threat was not the JL bu someone else disguised as them).
They could even set up Vibe as the Anti-Barry, making Barry the bridge between what we see and what we don't see (the JL...as Barry could hint at being friends with some 'special guys).