If you have a thing you know will almost certainly exist and be important in 3 years, you don't need to do a TAM analysis, sometimes it's just "in three years, if this succeeds as we realistically expect it to, would we high five?" and if so, then do it!
The hard part about this is the "realistically" part.
It's important to make sure you actually have a grounded understanding of the reality, and aren't just taking your own kayfabe too seriously.