I was thinking more along the lines that UGC may be added first so that we could have our own Starbase missions (ultimately, it's a more powerful tool and "free" content generation for players).
Honestly, I think Stahl would love to see all of it finished and out being used right now if he could. I would surmise that he's got teams working on both those things already (as well as teams working on a few other things they've talked about like Territory War functions, etc.); if that's the case, him saying that the UGC engine would probably come out sooner would then likely hint that such an engine will be faster/easier to code, test and release.
Again, just my thoughts Either being released would be awesome, I have some plans for the UGC engine already :p