I don't understand if we are supposed to be writing rules or heuristics here. Rules seem too heavy handed, and it's too easy for non issue cards to fall into that category. If I wrote a rule that said "RESTRICT: Any instant, sorcery, or artifact that can be cast for 1 or less mana that draws you 2 or more cards" then you would restrict Gush, DDT, Ancestral, TC, and the like but you also restrict non issue cards like Shared Discovery, Visions of Beyond, and thoughtcast. If I change the rule to 3 then suddenly I'm not restricting DDT or Gush, 2 cards that are pretty universally ok to be on the restricted list.
My point is that if we write rules to account for the current restricted list, as opposed to starting from a clean slate, we're still going to wind up with several rules that have unintentional splash back, or overly catered rules with a lot of pedantry.
I think as a heuristic, what happens is you can make a whole slate of rules as to what cards need to be watched and have a potentially shorter road to restriction, but it does not have to be hard and fast that the card is just removed outright.