If Deadpool is being introduced into the MCU, it likely won’t happen until sometime after the current slate of projects are done, which are currently scheduled into early 2022.
If the Deadpool movie is a standalone thing, then it could be inserted in the current slate without disrupting anything.
The one benefit of not including Deadpool in the MCU is that we might get a new movie sooner that way.
It also probably won’t happen until the rest of the X-Men are introduced into the universe.