It'd be nice if they merged them by leaning on firestorm screw something up, and supergirls city, and some others from her time, come over, but not metropolis, etc, and thats it moving forward.
They have a quick scene with superman saying they caused so much damage with it happening that they won't be able to fix and its better to mend what they have in place than try to fix it in it's entirety.
It would be kind of cool in the sense that all stories could simultaneously tie in to each other, but can be still geared to just there city.
It'd let Kara go through a whole creating the symbol as her own arc and no longer in supermans' shadow.
Arrow himself is fully fleshed out after this season..everything else i feel is a re-hash, so could allow for a different sort of political setting where maybe the world doesn't want someone like him operating.
And Flash, well...they kind of kick the bucket everytime so it'd be like every other season, and the merger of sorts would give LoT lots to do.