Mechanical. My pocket reference book (thanks WFH) says “the American Wood Council recommends limiting cantilevers to 1/4 of the allowable span for the same joist spacing” ...so even if you throw in some tight joist spacing you’re going to have less than 4’ allowable cantilever and less than 40lb/ft^2 live load with pressure treated southern pine. Additionally, I’d think the bending moment would get you (even if you put the crown up). Your deck would sag and be uncomfortable after a few seasons in the elements. Use metal. Heck use some quality channel shapes and you’ll have a cantilever deck that’ll support a 1000kw generator and day tank, for a mini-split AC, WiFi router, and beer fridge. Side note: My favorite blind as a teen was a loosely cobbled together deck from discarded pallet wood nailed to upper branch of a cottonwood tree precariously rooted to a 10’ sandstone and gypsum cliff. *sniffs* “yeah, that oughtta hold’er”