Hogwarts Future Works: A History
Let's first look at the questions that inspired the original Future Works discussion.
With the exception of the Magneto question, all of the questions are ones with blatantly obvious answers if the OP would just wait until the work was released. Until that time, the best we could do is speculate - sometimes good, logical, informed speculation - but speculation, nonetheless.
Some of these questions were generating a lot of back and forth discussion for absolutely no reason, other than the fact that we were discussing things based off of intentionally incomplete information. OPs were asking about things in trailers, and about movies which hadn't even been written yet.
We knew for sure that just waiting until the movies were released, we'd learn the plot of Star Wars Episode 7, or why Batman and Superman were fighting, or how the X-Men would defeat Apocalypse. By waiting, we could also pretty safely bet that we'd learn more about the Hulkbuster's pilot (though, this was kind of moot since we already had leaked information that answered this), or get a better explanation as to how Magneto was pulling Mystique. All we had to do was wait.
So, we created the Future Works Policy, shunting these sort of questions until a later date.
"We might learn the answer later" vs "We will (almost) definitely learn the answer later"
In today's world of reboots, revivals, and sequels, the fact is that almost any question could theoretically get an answer at a later date. We shouldn't just close questions because they might get an answer later. We need some sort of likelihood of an answer. It's important to remember that not everything is a Chekhov's Gun, and may not be addressed later.
Franchises like Star Wars have sort of spoiled us. Every character has a backstory, and on a long enough timeline, just about every character will have their backstory written about, no matter how fleeting their part in the movie. But we don't know for sure that we'll ever learn what age Biggs and Luke met. Maybe we will, maybe we won't. To date, there has been nothing to indicate that we actually will. Conversely, as I understand it, we do have ample reason right now to believe we'll learn how Han Solo and Lando met (I haven't watched the trailers, myself).
Similarly, the Russo brothers have promised that we'll get a better explanation as to the whereabouts of Ant-Man and Hawkeye at a later date.
It's OK to admit that we just don't know
We established long ago that questions without canonical answers are just fine. Sometimes, we just don't know the answer, and it's perfectly ok to say that as an answer. Logical Speculation is ok. If it's not Future Works, answer to the best of your ability. That might mean saying, "based on these canon bodies of works, there's just no clear answer" or "nothing definitive is ever stated, but there's strong evidence pointing to [this]."
So what's the difference? Where is the line?
I'd say that anything based on trailers, specifically about announced works, or otherwise outright promised by someone authoritative that we'll get an answer later would be defined as Future Works.
Questions about elements merely set up for possible later attention or answer should not be defined as Future Works.
Future Works: How will the ending of Infinity War be dealt with in Avengers 4?
Not Future Works: Where did Groot get his video game?
Future Works: Why does Cable want to kill the kid in Deadpool 2?
Not Future Works: How did Wade Wilson become a mercenary assassin in the XCU?