I use a spring rate of 0.55kg/mm in my Suzukis. I use 0.55kg/mm in my BMW.
Overall length of the USD Showa is within 40mm of the standard BMW. with my Ohlins rear shock being higher than standard, it'd work fine with the forks raised maybe 20~30mm in the triples.
The standard F8 forks are shit. Pure shit. The one reason I don't like riding it off road.
Steering stem height is the same, bearing ODs are the same. there's no reason it can't be done. Brakes is the only significant hurdle, because of the abs, even that is do-able with the right approach.
All that remains is to do it.
Valving wouldn't even need to be changed. Put a set of 0.55kg/mm springs in a set of Showas, use billet triples and fit it all up.
I prefer the Showa dual chamber conventionals for Adventure bike applications, purely because they hold far more oil and are not prone to spewing it all out when the seals wear. yeah, they leak, but you can live with it for months. Not like USDs when they do start leaking.
With the Showas, there's spares out the wahzoo. Common as brown dogs.