2.5 future potential features

BIO (block I/O) I/O subsystem API rewrite (one single bio is enough to do I/O in more than on page)
even higher SMP scalability (io_request_lock just gone, Read Copy Update)
scalable scheduler multiqueue possibly decreasing the current O(NR_tasks_running) complexity
async-IO
x86-64 merging
preemptive kernel (maybe, probably not)
further (last?) analysis of reverse pagetable maps in the VM
large pagetable support?
page coloring?
more/better drivers as usual :)
...