The limit will generally be the voltage regulation int he ESC, which powers it's logic circuits as well as the BEC output to the receiver. Novak has typically limited the majority of their ESCs to 10 cells (conveniently, 12V nominal), which is pretty reasonable. Tekin used to go from 10 all the way to 32 cells (38.4V!), but their ESCs had specially designed BEC circuits, or specified external receiver packs at high voltages.
Recently, I've seen a lot of controllers that only do 6-7 or 4-8 cells, which I find a little bit disappointing.
With modern ESCs, <=8 cells is a practical limit, with 10 being possible using ESCs that support it.