There are not so many limitations in the OS design. It most likely will never get any secure runtime multiuser abilities and memory protection will never reach a level considered to be safe enough compared to other systems. It will always have one address space for all applications, but this limitation should be no problem anymore with 64bit pointers, as the 16 Exabytes address range should give you enough space to enlarge stacks for example. Currently not even started, but possible.
So there are possibilities to reach a certain level and if some hero steps up (which happens from time to time) speed can increase. Currently progress is slow, so the gap to modern systems doesn't get much smaller.
But for a developer this might be the challenge, push the limits further and further. That's what the Amiga always was, back then maybe with demos etc. Now there is an additional challenge for OS developers ;-)