It's possible Teoscar averages 4 WAR/yr for the next 5 years. It's a very unlikely outcome though.
He's got a .348 BABIP in 2020, and rocking a .375 BABIP so far in 2021. Those numbers will regress.
Extension decisions cannot be made on an individual player basis. Shatkins has an idea of the max budget Rogers will allocate to player salaries. Just like any organization, need to look at the entire team and project values for each player going forward, using aging curves, etc. We all know the Jays have a bunch of elite young players that will be elite for much longer than Teoscar. Those players are the priorities for signing long term. And I am sure the Jays have allocated a hefty amount for FA signings, particularly for pitching. Where Teoscar fits in the team budget calculus, who knows. But I suspect there is a good probabiity he is traded / not extended.
In fact, trading Teo after this season would be a classic sell high move.