Actually, since Intel Pentium 686 (I think), there is an upper limit of 64GB of RAM. Likewise, most OSes can address that as well, however it depends on various conditions and has its own limits.
Also, as you say memory controller is integrated with CPU, so modern topology of motherboards usually has memory connected directly to CPU, bypassing chipset. Also, it's why most topologies connects at least some of PCI(e)'s to CPU directly as well (giving GPU access to system RAM). This is also, accidentally, why good VGA requires good CPU as well for it to perform satisfactorily.
Anyway, what's really limits the MAX_RAM on the system is motherboard. 4GB requires 32 physical paths for addressing (excluding data, it's just for addressing) from CPU to memory slots. 8GB requires 33, 16GB requires 34 and so on. Intel's CPUs currently have 36 addressing pins (at least).
But laying pathways is expensive. Cutting down on this work lowers costs and in result prices.
So basically only limit is in motherboard...
However, sometimes documentation lies (unintentionally). It may be a good idea to try (if you have access to free ram for testing). OTOH, this was more common in days past. I don't know how that works in new/newest products.
EDIT: of course, I talk about POSSIBLE MAX. If manufacturer will not implement them in the chip, they won't be available. That's why there's max amount of memory supported by CPU usually way lower than 64GB. Anyway, what matters is CPU limit (pins and IMC to be exact) and motherboard (physical paths CPU-RAM sockets).