There are some relatively ancient graphics cards supported by fbdev with no KMS driver. They may need to use the simple framebuffer-only support (simpledrm). I believe almost no users will be affected by this.

simpledrm expects somewhat sane framebuffer memory layout which many of the ancient cards cannot provide so even that probably is not a solution. But the problem is non-existent because in PC context these cards are ISA cards made well before 1995.

Most have been using DRM/KMS for years now, so there won't be any noticeable change for them.

It won't.