You'll likely end up with a "discount" B fare that entitles you, as a non-Premier or a Premier Silver, to an Economy Plus seat, and as a Gold or higher entitles you to absolutely nothing(*).

Yet the fare will not otherwise be treated like a "B" fare, such as for instant upgrades and (I suspect) things like Star Alliance mileage based upgrades from other carriers' mileage programs (normally only Y/B fares can be upgraded this way).

(*) It is unclear if the upgrade prioritisation is based on B or the underlying cheaper fare class. If the former is true, this is actually a pretty good deal - a 1K on a B fare has a high chance of getting an upgrade. I'd probably pay for the fare differential for that on some routes.