The implicit premise here is that your website requires HTTPS only and that a theoretical downgrade attack is enough to justify not having http at all.
Most websites don't even need HTTPS and the complications and sacrifice of autonomy required isn't worth it. Remember, there are no cert authorities that are human people. They are all corporations or institutions. Having to get an incorporated entity's permission to communicate will have dangerous consequences eventually. HTTPS everywhere is done with the best of intentions but it will be the centralizing push that provides juicy targets for government and corporate censorship.
I'd flip that and say you should only support http if your website absolutely requires it. Unless you absolutely can not avoid supporting old devices you should just redirect http to https.
The privacy of all users is more important than supporting the outdated browser on an ereader.
Most websites don't even need HTTPS and the complications and sacrifice of autonomy required isn't worth it. Remember, there are no cert authorities that are human people. They are all corporations or institutions. Having to get an incorporated entity's permission to communicate will have dangerous consequences eventually. HTTPS everywhere is done with the best of intentions but it will be the centralizing push that provides juicy targets for government and corporate censorship.