The potential for clans of Force users to now form independently, for particular traits and styles to develope free from Jedi and Sith doctorines, without being classified as either one? All the dynamic variations that become availble to story and character which are now far more unpredictable ,
This is why you can't discount 'ending the jedi' or sith or grey jedi or anything else.
Per the Clone wars, apparently the jedi had a system of identifying all children born that were force sensitive. Even under THAT system, there were still able to be 2-3 dark force users out there that the jedi were blissfully unaware. So, it's very possible they don identify 100% of them? In TPM they referred to some who quit the order. What are you if you quit? It's not like the remaining Jedi can make you never able to user your abilities again. So, at that point, you're neither Jedi or Sith. Furthermore, Jedi isn't actually a given either. It's literally more of a private club. You have to abide by their rules, or you're denied membership and instruction. Jedi and someone who uses the light side of the force aren't mutually exclusive. You CAN be someone who uses the light side and NOT be a Jedi. Same thing on the sith side. You can use dark side abilities, doesn't make you a sith. Then again, nothing has ever said what it takes to be sith. Case in point, Kylo. Post ROTJ, Master AND Apprentice were killed. No one's left to proclaim anyone sith. So, Kylo is a just a dark force user. But there's nothing really stopping him from calling himself a Sith Lord. He's so into grandpa i expect him to do just that in TLJ.
Now...flash forward from post ROTJ to TLA. Luke has no method of tracking children born force sensitive. That system is long gone. He also has no clue WTF a midichlorian is (thankfully). So, in theory, there should be a lot of force sensitives out there that have had zero training or are totally oblivious to the fact. What are they called? They're clearly neither Jedi or Sith. Yet they're out there. Luke 'had' and academy, therefore the universe is still producing force sensitives.
You can quote supposed rules, but, they clearly are completely fleshed out. And while we're at it - Hidalgo can say there are no grey jedi, but that could very well mean there's no group called the grey jedi. Or it could be a lie if it's supposed to be a movie reveal. After all, Rebels is canon, and Bendu is neither jedi or sith and clearly much more powerful. So there are definitely more classifications out there.
I'd love for Bendu to show up to teach luke about the other path (or one of the others) - his teachers would be Obi, Yoda, and Tom Baker