I'll tell you what'll limit the production of a 5.5" iPhone model - there ISN'T going to be one.
Raising your hopes for an imaginary product, based on imagining that product into reality may feel nice in your head, but for a product to be sold, it has to physically be made, and I express very strong doubts that Apple are going to be the ones seen to release another surfboard phone. Just because Android vendors produce clown-sized phones, doesn't mean that Apple - the company with their OWN timeline and who aren't rushed or pressured into product ideas by outside influences - are going to make something equally sized, just because the mainstream thinks it's a good trend to follow. Making a certain sized phone "just because everyone else does it" is not good business sense.
Apple don't follow the trends, they forge them and *others* follow. Huge phones are huge and stupid looking (buyers will never admit this - it's called pride, something people hate admitting to, as the [perceived] "usefulness" of the large screen, to them, outweighs the clumsy, ugly stupidity of holding an ironing board-sized device to your face), and Apple aren't planning to make a fool of themselves just because X, Y and Z vendor copied Samsung and their inane ideas to create more SKU codes.
In case you missed it @ D11, Tim Cook stated clearly "We don't make the most, we make the best". A huge device may be popular, but consumers DO NOT know how to articulate, clearly, what they want, and will tolerate some shortcomings if the few benefits outweigh them for a period of time... but do you want customers to ADORE your product, or "tolerate" it?