I can't imagine it would be a simple as switching. Bostrom's teams, as well as Haga's, are saddled with the Dunlops for the time being. Their only option is to develop the Dunlops.
Also, it was the switch from Bostrom's "beloved" Dunlops in Y2K that almost did his SBK career in. I am not so sure that Bostrom would endorse any switch.