Sleeveless motors have been around for many years! Single/Twin and Triple Cylinder Snowmobile Motors come to mind as does the 1800CC Suzuki M109. The fore mentioned motors use chrome plated cylinder bores with cast iron rings. This combo allows the rings to seat and not the cylinder walls. So hard is the chrome that chrome/molly rings will never seat. With Honda's reputation for motor design/building you can bet the new flat six has many, many hours of dyno and bench testing.