***Disclaimer: I do not 1000% believe we will or should sign Brady, but the signs are there, and it does make some sense for both sides.***
Why the Niners would do it
A couple of reasons here, with the biggest being that they don’t believe in Jimmy G. Again, I am not saying that I believe that the Niners have lost faith. Still, there is one glaring fact that leads me to believe that this is a possibility: they have not publicly come forth and denied the Brady rumors. They will continue to say that Jimmy is their man - and that may be true - but the dreaded ‘vote of confidence’ is also often given to players and coaches before parting ways. So while it would be incredibly easy to say ‘we are not interested in Tom Brady or any other QB, Jimmy is our man,’ the fact that they have not shouldn’t be ignored.
Also, the Niners are currently in a ‘window’ to win a ring, and they should do what is needed to increase their chances to do so. If they believe that Jimmy is holding them back or that Tom would give them a better chance through the next 2-3 years, then they should pursue him. Additionally, next year’s draft could be used to address the future or traded out to stockpile picks for the 2022 class to take their future signal-caller - let a rookie sit behind Brady for a year or two a la Rodgers or Young.
Finally, it would allow for additional draft picks when trading away Jimmy (New England to reunite him with Belichick, who reportedly loved him as a player and person) as well as salary savings. In essence, Brady would not be cheap, but 1) would be less than Jimmy’s current contract, especially if the SB was stretched over five years and 2) would only be for 2-3 more years. Extra draft picks in, say, the 2nd and 3rd round would go a loooooong ways towards replacing what was given in trades, and the extra money means retaining or adding talent we otherwise couldn’t.
Why it makes sense for Brady
If Tom really does want to prove he can do it without BB or if the Pats have simply decided it is time to move on, then appealing options are very few and far between. He’d ideally want to go to an immediate contender and would likely want a favorable living situation as well - tough to imagine Brady and Gisele moving to Jacksonville. SF provides the best of both of these requirements, putting him on a team that should have won a title last year and in a great area to live. Tennessee doesn’t offer the lifestyle, and the Dolphins or Chargers don’t offer the football team built up around him. If the Niners are truly interested, Tom will leap at the chance IMO.
So, even though this entire site has nearly universally decreed it to be an outlandish idea even to consider, IMO it is well within the realm of possibility. SF has not squashed rumors, there are advantages and benefits to making the QB swap, and from Brady’s end, it would be a home run.