In my opinion, this question title is a borderline case where it may be a bit spoilery (I don't think it's that big of a spoiler), but we will have to live with it either way.
Lets take the commenter's points one at a time:
- It's been almost a month since TFA was released
Based on our previous spoiler discussions, this is actually irrelevant. The general practice, as far as I can discern from reading back through meta, is that spoilers never expire; if it's a spoiler on release day it, it's a spoiler a year later. (the trick is defining what exactly is a spoiler; see #3 later).
- People can add TFA to their ignored tags to avoid spoilers
Unfortunately, not true. The reason we are much more strict on spoilers in titles than in question bodies, answers, or comments is precisely because this isn't true. There are any number of ways that ignored tags can get seen anyway: the Hot Network Questions lists, the chat feed bot, the mobile app which ignores tag preferences, the twitter feeds, etc.
- I feel that this question doesn't spoil any major plot points
This is where things start to get complicated. We have never been very good at separating spoilers from stuff that happens in the movie. Not every plot element, action, or line of dialogue from a movie is a spoiler. (There are some people who do generally want to avoid every detail about a movie, but I would claim that goes well above and beyond just avoiding spoilers.)
The generally accepted definition of a spoiler is something that, if you knew it before hand, would literally ruin ("spoil") the movie for you. That's what we need to ask ourselves when we decide if something needs to be hidden as a spoiler or not: if I knew this going in, would I have enjoyed the movie less?
In this case, I would argue no. Luke was entirely absent from the trailers, and his absence was noted very early on. The very first line in the opening crawl is "Luke Skywalker has vanished." The rest of the movie is driven entirely by the search for Luke's whereabouts. It's pretty clear right from the opening second of the movie that Luke isn't going to be around. Knowing that he remains absent except for a little bit at the end, in my opinion, doesn't detract from the movie in any way.
- The question title was way to vague in spoiler-free form
This one is really at the heart of the issue. Question titles need to be meaningful, and in borderline cases, this is often the deciding factor.
If you can come up with a way to phrase the question so that someone else asking the same question can still find it, without revealing the plot detail, that would be perfect. That's the ideal we strive for as often as possible. In this case, I've spent a few minutes trying to do that and come up blank. We absolutely don't want titles like "Why did Luke do this?" -- those are useless.
Until someone can figure out how to reword the title in a meaningful way without including that particular element of the plot, I think it needs to stay as it is.