So they have these options for the Joker
1) Batman prequels - Leto, DCEU current timeline - Leto
2) Prequels - new actor, DCEU - Leto
3) Prequels - new actor, DCEU - new actor
4) Prequels - Joaquin, DCEU - Leto
5) Prequels - Joaquin, DCEU - new actor
6) Prequels - Joaquin, DCEU - Joaquin
If Reeves shoots Batman next year, release it for mid 2020, takes a break and do the Netflix deal starting 2021, return to helm Batman 2 involving The Joker, from 2022 and shoot it 2023, release 2024...
...then we potentially have BOP (2020), SS2 (2021?), Batgirl? (2022) and BOP2 or GCS and/or SS3 (2023), do they really need the Joker for these films? If they do for some of them, it won't start to get awkward until 2023 when Reeves starts to shoot a sequel with a an actor not called Jared Leto, before that, Leto will be the official Joker...
There are many ways this will go down, egos, contracts, Reeves/Joaquin's willingness...but my preference would be - Joaquin for his own movie and Reeves' movie(s), Leto for all the current timeline films and doing a better job under different directors and writers
and they can just make Leto's Joker a different person to Joaquin, and I'd use the same Batman actor for Reeves films and current timeline as Affleck won't be back so it's a straightforward replacement, so when Bat meets Leto's Joker in the say SS2/3 or Legion of Doom one day, it's just a different Joker so they don't need to say stuff like "oh, you look different" or explain the completely different behaviours, they did do the 3 Joker thing in ?Rebirth? Just quickly explain something.
This should keep Joaquin happy as he's only doing 2-3 films max and Leto keeps his roles maybe even as main villains in SS spin offs/team up films.