Lol.
Not that it really matters, but it's easier to SDI out of Fox's Fair than Wario's Dair, at least for me anyways. Each hit of Fair has a larger SDI frame window than Wario's Dair, letting you input more directions per hit than Wario's Dair. Not only that, but in the instance where an opponent SDI's out or Fair/Dair, Wario can chase them/follow them better during Dair than Fox can with Fair.
Say I hit someone with Dair, they SDI out to the side. I drift Dair back over to them since Wario doesn't have a problem moving one direction quickly or even changing directions on a dime. If I Fair with Fox and Someone SDI's behind me, I'm not gonna be able to catch them unless I was already like retreating with Fair in the first place.
As for Fox's Dair vs Fox's Fair, depends on if they are short hopped. Short hopped Dair is kinda easy to SDI, but there's relatively little risk to Fox if someone escapes. SH Fair is a bit harder to escape, but there are a lot of characters who can punish Fox while he is still in his attacking animation once they escape.
Those move comparisons are not really an important facet of the matchup, but I felt I would get that out of the way.
As for Wario vs Fox, I like the matchup. It forces both characters to think a lot, and neither character has a dominating aspect or overly safe approach/kill move. I would give a slight edge to Wario in safeness, mobility (air only) Killing (both in power and versatility), and recovery. I would give Fox a slight edge in attack speed, ground mobility, and overall range (It's not like Marth vs Wario where it's an all out spacing war, and yet it's not like Sonic who has to rely on his speed entirely to get inside someone's range.)
I would rate it overall 55:45 to 60:40 Wario, 60:40 or maybe barely 65:35 (Only if the CP was just ridiculous for Wario, which I don't see one like that against Fox) Wario being on one of his CP stages like Rainbow Cruise, and 55:45 being a really close neutral.