I know you are possibly no longer interested in this, but this was a good question, so here is my answer: X means all possible products in the cart (with same id).
For the remarks below I ordered 10 "WG-5569" products with your implementation and 11 with the current one.
I have finally decided to not apply your patch. Because I found a regressive bug: if you use "Order Percent Discount" you get a lot of unrelated promotions. BTW same issue for "Order Percent Flat". This works well with the current implementation, where you have to take into account that only the "Is Greater Than" operator is always used, see my comment above on how to define the action rule.
I will change the UI to explain what the current implentation really does: it always and only uses the "Is Greater Than" operator. WIth this information in the UI people should not be confused. Anyway with this operator you can easily do a "Is Greater Than or Equal to" operator by changing the "condition value". For instance if you want a break at 10 put 9 in the condition value, etc.
I noted also that when using "Gift with purchase", it's weird in both cases: if you ask for 1 product you get 8 :/
I will close this issue, if someone wants to improve to allow using the other operators then another issue should be created. But I believe it's usable as is because the other operators don't make much sense (if any) with this rule condition. IMO, Only the "Is Greater Than" and Is Greater Than or Equal to" operators make sense with "X Quantities of Product".