The Recon in Force idea is disturbing due to the implications, but I still think its the most likely possibility. In both cases, the Nephilim basically 'threw away' the fleets that were involved. Neither fleet was large enough to take on Confed without support, and yet that appears to be exactly what happened.
There are a few different possibilities as to what might be going on at Kilrah. A few of the more likely ones are listed here.
1.) What got sent through the Kilrah wormhole was a sizable portion of the Nephilim fleet.
2.) The Nephilim sent their initial survey fleet through, found the Kilrathi and their shattered war machine, and sent word back to their home systems that a larger fleet would not be needed.
3.) The Nephilim fleet that appeared in Kilrah was a survey fleet designed to scout the area out while simultaneously causing problems for any enemies in the area (i.e. a Recon in Force).
4.) The fleet was a distraction to cover something else.
My thoughts on each idea are as follows.
1.) This idea would be nice from Confed's viewpoint, but doesn't seem to fit with the facts. If the initial Nephilim fleet was such a large portion of the Nephilim's fleet strength, then how could they afford to almost instantly commit another large chunk of it in Proxima? And there are also indications that the Nephilim might be in other systems as well.
2.) This idea has merits. Under this idea, the Nephilim invade Kilrathi space, and meet very disorganized resistance. They swiftly gain space control of a number of systems, and decide that there is nothing capable of opposing them in the region. By the time the Midway disabuses them of that notion, it is too late, and only last minute piece meal reinforcements make their way through the wormhole before it is destroyed. The problem, as I see it, is that if that were the case, then the Proxima invasion would have been much more powerful than the Kilrah invasion. The Nephilim knew they were up against a more powerful opponent, and yet the Proxima fleet appears roughly the same size as the Kilrah fleet.
3.) This is the idea I prefer, as scary as it is for Confed. Basically, the Kilrah survey battle group came through and got the lay of the land. They then proceeded to crush the Kilrathi resistance, and figured out where these human interlopers came from. The Midway then came and rolled them back. Fortunately (from the Nephilim POV), a system with a star suitable for powering a wormhole was discovered, and they launched a new expedition into Proxima space. The Proxima survey/ RIF was launched with the idea of figuring out the more minute details of the local systems that would not have been available from captured databases. The assault was eventually crushed, but it gave the Nephilim a great deal of additional information on their new opponents and caused numerous headaches for Confed. Not only that, but even though the Proxima wormhole has been captured by Confed, there are still Nephilim forces nosing around in two or three other sectors of known space.
The only real objection that I've seen to this is that giving the Nephilim that powerful of a space navy would put Confed in serious trouble
4.) A distraction theory is plausible, as well. The problem is that there are no clues at all as to why the Nephilim would have needed a distraction in the first place. What could be more important than a wormhole next door to Earth?
Comments, criticisms, and other odds and ends are, as always, welcome.