Everything is hypothetical at this point, but ComcastUni will want to wait until tourism is roaring back before opening a new park so they could maximize the hype and revenue. People need to have vacation money and feel comfortable about spending it. It will take a long time to hit those benchmarks, and until then, the existing parks will need something to draw people back.
For reference, Disney's current system is accepting reservations until September 2021. If everything goes according to plan and the pandemic ends around that time, things will be just starting to recover.
I doubt Comcast will greenligiht construction as soon as they have a positive quarter. They will want to see a year of growth or more before feeling comfortable pulling the trigger. So now you're looking at a potential opening date in 2025 or 2026. The two parks can't sit idle without new attractions for four years (Velocicoaster has next year covered).
Lastly, my understanding is Nintendo's contract stipulates their attractions must be built within a certain timeframe. Under those circumstances, Mario would have to move into one of the two existing parks.