I'll see if I can get one of the team to give me a solid answer, but as far as I know it is available to even the BASIC RIDER Tier.
The bike editor is something to mess with until the Sneak Peek becomes available. However, it will be a part of the full game as
well and from talks it *MAY* be attached to the Mobile aspect as well so you can design your rider/bike and import it into your
game.
EDIT: Just had it confirmed that it will be available at all tiers for new pre-orders.