Smart phones have reached a maturation point where the iPhone could easily release every 18 months and it would be totally suitable for the market. But Apple has investors to please, so that probably wouldn’t be the most likely scenario. With smart phones breaching over $1000 and in not the best of economic conditions right now, I don’t know that really makes sense to have an iPhone every 12 months.
I do think the numbering system though, will always be part of the iPhone. And the reason I think it will be, is the highest number iPhone shows the latest model, and it devalues the lower model, showing consumers the hierarchy chart. That said, I don’t suspect the numbering system will leave anytime soon.