There is precedent now: several states have rolled back motorcycle helmet laws.
I think you'll have to start with congress with this, as mandatory seatbelt laws were attached to highway graft distributed by the congresscritters after having been stolen from the taxpayers. If they don't have mandatory seatbelt laws, they'll lose some portion of highway funds. As long as that is the case, it will snow in hell before the laws are repealed. Its always all about the money folks!