Not to derail the thread but I do find it hard to reconcile what you just said there with what you previously said (in a now closed thread) about TCOE potential new methodology for race and class features. Like I said not trying to derail this thread or drag up the other but it leaves me even more perplexed about the previous conversation.

I think a minor benefit like a skill proficiency or some other thing that fits the feat's theme could work. It would mean you would have to brainstorm what that minor benefit would be so its a bit more work on your end as a DM though. What is the feat in question that your player is considering? Maybe the fine folks here can give more specific advice on changes to said feat that way, or if the feat might even be good enough to not need a minor benifit.

If I may add a little something to this conversation,

Sometimes players do have their PC's progression all mapped out from levels 1-20 at the start of a campaign, but once the actual play begins they might find that the reality of how their group and character dynamic differs wildly from their expectations, in which case decisions made early on might never be used even once (lookin' at you, True Strike)

If a DM wants to be a stickler for the rules as written, that is entirely their prerogative.  However, if a DM decides to allow leeway for players who find that their plans for their characters have changed, letting them make some changes to course-correct their character will not break the game.

@sardonicmonkey:  Ugh, please don't bring that trash thread over here.  I already noped out of that ridiculous conversation, I don't want to see it spread to others...

One thing I want to clarify regarding my player is with respect to "planning their character out ahead" For the first half of my campaign, I was running Curse of Strahd. To maintain the balance of the module, I was more strict about what characters could be or could do, with practically no homebrew added in. Now that the part has finished Curse of Strahd, I am continuing the campaign in a different setting where I am designing the encounters (specifically, I supported the Grim Hollow campaign setting on Kickstarter and am using that for my more "homebrew" setting). Because of the new setting and me now moving to be more lenient on homebrew, the feat that my player wants to take was NOT available to him when he was first designing his character.

So, tl;dr because of a switch in campaign settings/modules in the middle of the campaign, my player had no way of planning ahead for the feat he wants to take. 

Thank you for all of the suggestions so far. I am going to think on this some more, but I just wanted to clarify that this isn't the player's fault for not "thinking ahead" with his character design, which is why I am leaning more towards giving him some (minor) extra thing.