EXO can comeback Q2 2021 soonest bc Xiumin is only returning Dec 2020 and Kyungsoo on Jan 2021. Unless they won't wait for D.O., EXO can comeback Q1 2021. Depending on the weather in Korea re: Chen and the CHN-KRN political climate re: Lay, at least 5 members are ready Q1 2021.

Baekhyun will enlist mid 2021, so a tour is also not possible even if Kyungsoo joins the ranks, since Chen and Chanyeol both have to enlist later 2021. This is when a possible EXO sub-unit OR collab group (EXO member with another SMTOWN artist) may arise with '92 line away.

Xiumin, Kyungsoo, Kai, Sehun will be the only active members left for 2021-2022. If CHN-KRN political climate has relaxed, expect Lay to return and resume with Korean promotions. With Lay, they might be able to release another comeback later 2021-2022 as 5 members.

By 2022, we will finally see Suho back by Q1, and depending if SM scattered 92 line enlistment or letting them enlist together, Baekhyun at least will return late 2022 (and IF PCY and KJD both join him, it's around that time). We can have an 8/9 member line up by Nov/Dec 2022.

Hoping the political climate is finally okay by then so Lay can promote with EXO again. With this, EXO may tour again late 2022 and when 2023 comes, however, without Kai (if he is still required to enlist) and later on, without Sehun. So 2022 is the earliest we can see OT9 again.

With all these details, you can alr roughly infer when EXO can release an album, when members can release music (as soloists/subunits), and when they can tour. The roster of active members is important. So at least, next year we can have either a comeback or new subunit, or both.

And this can happen early 2021. They will probably wait for Kyungsoo so I am gunning for Mar 2021 without Suho and Lay (and maybe Chen if he enlists early or if he doesnt join the comeback). However there are recent talks about the easing tension so we might see Lay back.