The next process node would be 22/20nm. However costs today are much higher per transistor than 28nm. That combined with a new NRE would make 22/20nm miners uneconomical today. To date only Intel has released product using 22nm process and Intel doesn't use foundries they built their own custom fabs to their own specs. It doesn't look like 2014 will change that much. A couple companies are looking to do some production runs of cellphone chips @ 20nm. Remember cellphone is a perfect market for this as the higher chip cost isn't really that important but improved battery life is. General purpose fabrication @ 20nm is probably not going to happen until 2015 and any miner you buy today will either have made a profit or never will long before that.
Things you should be thinking about:
a) Bifury, Avalon, and ASICMiner will move to 28nm eventually. Bitfury 55nm chip has better efficiency than some 28nm designs. What will its 28nm design bring.
b) Miners are bad at math. They may collectively buy hundreds of PH/s of capacity. So much capacity that collectively miners lose (total hardware cost + total electrical cost < total mining revenue).
c) Lots of room for falling prices @ 28nm. Raw silicon is likely $0.25 per GH. The material cost for an entire rig is likely $1 per GH. That doesn't mean you will see $1 rigs but prices can come down a lot.
"b" is the one to worry about. You can't control it so your potential fortunes (or losses) are highly dependent on the actions of someone else who may be utterly clueless.
If you are still worried about 20nm, remember
just because a process node exists doesn't mean it is the cheapest way to produce a chip. Mining is very capital intensive. Miners are constantly looking for falling prices not rising prices. It generally takes two to three years before a new process node becomes cheaper than the prior one. Worse this process seems to be "slowing down". The cost improvement when mature from one generation to the next is getting smaller and the time it takes to mature is getting longer. So it takes more and more years to get a smaller and smaller gain. These slides are from a presentation where NVidia was "complaining" about TSMC's 28nm process last year but the the general theme is applicable to 20nm and beyond. Even NVidia (with annual volume in tens of millions of units) doesn't project their cost per transistor on 20nm to beat 28nm until Q1 2015 and 14nm to beat 20nm until Q1 2017.
