I just discovered the "portrait of an uber" thread from a couple years ago, and it has contributed greatly to what I believe is my final conclusion on Keldeo.
One of the specifications discussed (and approved of) was the ability to sweep without putting the pokemon or team at risk. I believe this very much captures keldeo, this particular sentiment even moreso than something like excadrill.
Whether we are talking about scarf/specs/ebelt/etc., keldeo has counters and checks. Let us digress for a moment and look at the counters and checks for something like Terrakion. Ignoring the SD set for purpose of comparison (since it is then a difficult case to compare to keldeo given how less useful a boosting move is on it), common terrakion counters/checks are lando-t and skarm. If one of these pokes comes in (bar hp ice for lando ;) @
Spinda), they force terrakion out but in the process they are able to set up hazards or, in the case of lando, either hit the switchin very hard or u-turn. If we were to look at keldeo's common checks now: jellicent, latias, celebi, we would see that while these are hard stops (actually not really, but that's for a different discussion), these pokes are also generally unthreatening and scream set up/pursuit bait. While terrakion's counters are able to inhibit terrak's team with hazards/etc., making it somewhat of a liability to try and sweep with, keldeo's counters do not ascertain pressure, rather they force keldeo out right into a good matchup against said counter with not much harm done, meaning that keldeo has significantly less risk when using it as opposed to other top tier ou mons.
Another concopt that was brought up was the ratio of how much damage it can do to how much it can take. This time we will compare two controversial pokes: keldeo and kyurem-b. Now obviously kyurem has crazy power and bulk, but that isn't all that the sentiment was covering. A major part of it was soft damage. Kyurem is stealth rock weak, spikes weak, priority weak, sandstorm weak, has a rather poor defensive typing (in the grand scheme of things... Yes it gets switchin opprotunities but that doesn't make it any less vulnerable to a later scizor/rakkion/ keldeo/ etc switch ins. If we were to assume common battle conditions, Kyurem would have less than 75% of its health on its first switch in (rocks+possible sand, spikes, damage on switch in, etc). This, combined with the fact that many common moves are doing 2x damage very much so alleviates its great bulk. Keldeo on the other hand is resistant to sr, resistant to the most common priority, is weak to less common types. These traits, namely rocks and priority resistances, enhance keldeo's ability to "take damage" very well.
So it is for these reasons (among others that I dint care to post as I'm typing from an ipod) that I believe keldeo does indeed fit the bill of uber