OK, let's say 22 nm.
22 nm is only available to Intel, and they don't take outside orders.
23 nm?

Are you trolling? 23nm fabrication doesn't exist.
Available process nodes (full process size with half size in parentheses).
130nm (110nm)
90nm (80nm)
65nm (55nm)
45nm (40nm)
32nm (28nm)
22nm (20nm) *
* Nobody is making processors @ 22nm except Intel (not even AMD or NVidia). A couple of memory companies are using 22nm but memory is magnitudes simpler than a microprocessor. TSMC will begin early (i.e. insanely out the butt expensive) production of 20nm in Feb 2014.
Generally it takes around 3 years before a new process node becomes cheaper than the prior node. The only reason why cost effective 28nm Bitcoin are possible is because it is "old" tech, 28nm became available in volume production over two years ago, with early production in 2010. Following that 3 year timeline it would put 22nm/20nm not acheiving cost parity compared 28nm until ~2017.
So 28nm is as good as it gets for the near future. That doesn't mean we won't see improved 28nm designs but I would be willing to wager we won't see a sub 28nm Bitcoin chip (actually hashing in customer's hands) until 2017 and honestly I think it will be later than that.