Its currently impossible to create an operating system that supports unlimited RAM.
It has to do with maximum integer size recognized by 32bit systems vs 64bit systems. In simple terms, in a 32 bit system, the largest number that is recognized and can be used by software is 4,294,967,295. In a 64bit system, that is drastically increased to 18,446,744,073,709,551,615, which should be enough for RAM upgrades for the next few weeks.
Basically, 32bit systems ARE going to fall by the wayside, much like 16bit did before that. 64bit is eventually going to be the standard and 32bit systems will cease to exist.