It would be neat, but honestly the complexity of a modern CPU is not something that any individual would be able to recreate in a life time if they were building it piece-by-piece. I imagine that's true for any CPU capable of running recent Ubuntu releases or even something light like, I dunno, Puppy.
Actually, the complexity of a modern CPU is mainly in making things run fast. Building an in-order, no-cache, single-issue ARM capable of running uClinux doesn't seem all that difficult. The cycle time would be horrible though. You might not live long enough to watch it boot.