There's a difference between "possible" and "smart". It's one of the key reasons the Fort Lauderdale loop fell through. And that was with The Boring Company being willing to pay for the entire project. Same goes for Miami's proposed loop. One of their key reasons it's been in limbo is the concerns of chronic flooding, porous limestone foundations, and its low elevation near sea level.
We can debate until we're blue in the face about whether it "can" be done. But time and time again, they've shown that they aren't serious about moving forward with these projects. They've been having discussions about loops for nearly a decade and out of 14 proposed tunnels, they've successfully opened one.
I mean, some of these discussions are straight up ending in The Boring Company ghosting interested cities. Bexar County/San Antonio got as far as selecting The Boring Company to build one and it ended it the company leaving them on read.
I'll be absolutely stunned if this moves past the negotiations stage.