I find it difficult to speculate on this because I personally struggle with the whole "phablet" concept and am slightly dubious about the long term success of the 6+. I get that there has been pent up demand for it but I'm not convinced it's going to run away with the whole market for a smaller iPad.
At the end of the day there's a difference between wanting an iPad and finding the smaller size of the mini convenient, to wanting an iPhone and finding the larger size of the 6+ a good compromise. Personally I have an Air and will chuck that in a work bag and carry it most places, but my phone is an iPhone 5 and even the regular 6 has me wondering if it's a bit on the large side; for a phone I absolutely want something small that I can pocket in any situation and always have with me; the iPad is optional and I'm fine with that.
At the end of the day there's a difference between wanting an iPad and finding the smaller size of the mini convenient, to wanting an iPhone and finding the larger size of the 6+ a good compromise. Personally I have an Air and will chuck that in a work bag and carry it most places, but my phone is an iPhone 5 and even the regular 6 has me wondering if it's a bit on the large side; for a phone I absolutely want something small that I can pocket in any situation and always have with me; the iPad is optional and I'm fine with that.