Hiya.
Feats in 5e are about granting exceptions, primarily, with sometimes granting a minor bonus. As 5e's "bounded accuracy" works now, any feat created
must take this into primary consideration! If we end up with a half-dozen feats that all basically do the same thing ("Gives +1 to hit with X"), we will end up in the same boat that 3.x/PF is in (or, more likely, far, far worse...). We'll end up with "Fighter" and then we'll end up with "Fighter (Brute-Stabber-Build). The Fighter will have +5 th and +9 damage, but the BSB fighter will end up with +9 th and +16 damage with all attacks at advantage, at double range, and triple the normal critical range because of all the "feat stacking".
Don't. Do. That.
So...ahem...I'd be all for Feats that add character, flavour and interesting things. I'm against Feats that simply "stack on" bonuses. That way leads to madness! Madness I say!

Basically, a feat should give interesting choices for the character...not "flat, stackable bonuses".
For example, Thaumatuges (not picking on you, Thau, you just happened to write it all out nice an' purdy like...
GUILD ENFORCER
You are skilled at striking unwary or distracted opponents. You gain the following benefits:
- If you already have sneak attack as an ability, you gain an extra die when you use sneak attack, otherwise, you gain the sneak attack ability and do d6 damage in addition to your normal weapon damage when your target is unaware of you or in mêlée with another enemy (see Sneak Attack on page 27 of the Basic Game for a description).
- You can take a bonus action to take the Dash, Disengage, or Hide action. Once you use this action, you may not use it again until you complete a short or long rest.
The second point is good. It allows a "rule exception choice" to the player, it doesn't simply "stack on" something. The first point, however (as you noted), is up for potential abuse. It simply "stacks on" something that nothing else in the game does. What I might have done is have it work sort of like a "damage advantage" roll; you roll 2d6 for your sneak attack die, and use the highest one. It doesn't "stack on" anything, but instead uses a mechanic that is already in game (Advantage), modified, and doesn't really upset the BA of the system.
^_^
Paul L. Ming