I don't see them wanting to buff Steel defensively even more, and other than Poison I don't see your reasoning here.
In terms of likelyness, I would order them like this.
Poison I won't talk about, obvious.
Grass and Bug: Why would Fairies harm the nature they live in? Also, most Grass- and Bug-types are rarely seen in competitive play and those which are (both VGC and Smogon), have either great abilities or a great secondary typing, so I can see GF wanting to buff those types. However, I can easily see this being mutual in the form of Fairy resisting Grass- and Bug as well.
Normal: Same reason as they are immune to Ghosts; "Normals" don't believe in fairy tales or just a bit; NVE. Normals were also cruel to fairies. Humans were cruel against witches and other supposedly magical creatures - Normal SE against Fairy? Biggest reason not to change it is because GF might not want to change Normal at all, but outside of this, not much of arguing against this reasoning.
Steel is... steel. Fairies despise steel (weakness), and their magic does not affect it as much (resistance). Biggest counter-argument is that GF does not want to give Steel another defensive buff, as you just mentioned, but otherwise, much like with Normals, why not.
Electric: Static fields can block magic. Potential resistance. A bit of a stretch, but something that can be grasped onto if they feel the other Fairy-resists aren't enough.
I also think they don't want to have a repeat of the Dragon-type, so
I assume there will be something SE against Fairy that also resists it. Then again, I also doubt Dragon will be the only resistance/immunity of Fairy; I expect at least one or two more resistances unrevealed yet. Fighting, Ghost as well as Grass and Bug, and I have no clue how well Fairy takes Dark attacks (can be anything from SE to a resistance).