The 16GB limit is the real issue for me personally. There are plenty of Windows/Unix laptops that can do 32GB or more so all the excuses I've been hearing are ludicrous.
Increased power consumption with higher RAM may be true.
Presumably DDR3 and more important DDR3L have continues to improve the watts/GB.
Generally the CPU/GPU and LCD are the leading consumers of power on laptops. LCDs get somewhat warm, but have a large surface to dissipate heat from. CPUs on the other hand often need active cooling, where dimms (generally) do not.
Seems unlikely compared to a 28 Watt CPU and a 500 nit 13.3" display that the 16 -> 32GB upgrade would be particularly noticeable. Especially when apple claims that the low end and high end models have the same battery life, despite the low end model having a 10% larger battery and lower power CPU, GPU, less ports, and no touch panel.