[Q] Can the ROMs for different variants be flashed to thers? topic

I know Snapdragon won't work on Exynos and vice versa but on the older models the ROMs could be flashed from different international regions and worked perfectly - I used a UK ROM on my Note 3 for quite a while as the Aussie ROMs take as much time as tectonic plate movement to be released....
Has Samsung region locked the hardware through using region specific roms that aren't flashable through regions?
I see a few versions of ROMs around for certain 915* roms with the stipulation that they can't/shouldn't be flashed on another version and was wondering if that was so..
A Devs input on this would be nice, thanks for reading my ramblings...:p:D