I definitely don’t want to see too much of the CW Arrowverse brought into the comic book world but a few things would be welcome. Here are a few elements and characters I’d like to see in the DCU:
Alex Danvers - Supergirl’s sister has become a great character with a lot of depth. DEO Agent Danvers would be another strong LGBT character in the DCU.
The D.E.O.: With so many government agencies, this organization gets lost in the shuffle. The DEO in the comics should focus on extraterrestrial activity. SHADE deals with the paranormal, ARGUS handles meta human relations, and the DEO should deal with aliens. Having the Martian Manhunter as the head of the DEO would be pretty cool as well.
Cisco Ramon aka Vibe: Vibe has been completely shelved over the last few years. Over the years the “Big 2” have been trying to create more diversity in their respective universes. it makes zero sense that DC has a great Hispanic character appearing in their most popular show and they have completely forgotten about him in the comics. Vibe doesn’t need to be a regular in the Flash comics, but he could easily be a regular in a team book.
Aliens on earth: I really like how Supergirl has established that extraterrestrials have immigrated to earth. They still congregate in secret but Superman has become a beacon of hope for aliens trying to find a better life on earth. It could be the groundwork for what eventually becomes the Legion of Suoerheroes.