I just saw the announcement of a new Fedora kernel with this change note:
A large change over previous kernels has been made. The 4G:4G memory split patch has been dropped, and Fedora kernels now revert back to the upstream 3G:1G kernel/userspace split.
A bit of googling indicates that the 4G:4G patch is needed for systems with a lot of RAM (eg. 32 GB or more) because the kernel memory tables scale with the size of physical memory and a 32 GB system uses 0.5 GB for the table, half the kernel space available to a 3G:1G system. A 64 GB system won't boot because all of kernel memory is needed for the table.
Was this reversion done for performance or for some other reason? I'd guess most consumer systems won't need 4G:4G as they won't have anything like that much memory, and it only makes sense for an enterprise class server.