There is a subtle consequence of this change. I didn't realize the F High Deductible plan will also no longer be available in 2020 because it is a derivative of the F plan.
I really like the F-HD plan. The K plan is good but I think an F-HD plan from a solid insurance company is better.
I did a little more reading on and thinking about the F plan longevity. Even if I do enroll and have the F or F-HD before 2020, over time it is highly likely the premium for F plan types will increase more rapidly than for other medicare supplement plans, I write that because the insurance pool for the F or F-HD plan will shrink after 2020 as people die and the age demographics in the pool will keep increasing without "younger people" in the pool. Also, there might be new Medicare Supplement options available that are better price performance.
In the comments section of this post, a viewer was kind enough to provide information about what is being proposed by the National Association of Insurance Commissioners. In particular the "G" plan is being proposed to have a G-HD option:
This is a proposal. It could change. I also urge you to also pay really close attention to the new administration's actions regarding Medicare and make your voice heard if you do not like what is being proposed. Paul Ryan has for years championed a Medicare "voucher" system and is eager to make that change. If this administration adopts such a plan, it essentially means we will be given a stipend to go buy insurance. The government insurance pool (aka original Medicare) might be one of the options to buy but it's not known. If it will be offered, it's not known at what cost. If there is no government insurance pool, there is no need for Medicare Supplement insurance. I wince as I write that last sentence and will shout out loud and long to my representatives if it is proposed.
I have no crystal ball. I am keeping my K plan because it is a good price performer for me for right now and I will intently watch this evolution. I also live in a state that allows me to change my medigap any time to be effective the first of the next month. If your state doesn't, take action and press your state legislators to change the state laws regarding Medicare supplement plans.