I'll preface this by saying I've never worked as a repair tech for Asus, this is just based on my experiences working at a repair depot style shop that is, quite probably, very similar to Asus' operations.
This sort of thing happens. Where I worked, I was the lone Apple repair person for probably about half of a national retail chain, and it wasn't uncommon for me to have to basically annex space on the shelves of people next to me I had so many units. I routinely had a backlog of just customer units that was 2+ weeks, and that didn't count the "store stock" units which were stacked up all over the place, literally overflowing into some of the walkways.
So it is not surprising to me at all it might take this long. It's easy to get caught up in our own little world and forget that there are probably only a dozen or so people working at any given repair center, because if you have many more than that there simply isn't enough work to keep everyone busy. And sometimes there are part shortages. I know one time I needed the enclosure for a unibody iMac, and just as I needed it, Apple was suffering a severe shortage of that part (I only got that much info because I made nice with a couple of people on the administrative side of things who might pass me a little additional info, the only official communication I ever got was that my order was being canceled). I think it was probably the better part of a month before we could get that part and fix the unit. Some of that has to do with the way Apple abuses its ASP network, and I tried getting pretty creative, even going as far as checking gray market parts dealers like Blue Raven and MPD, which would be a violation of the ASP contract with Apple.
Whole books could be written on the complex interconnected interactions at play here, but let's just leave it at this: I can pretty much guarantee you that there is a technician somewhere, with your unit assigned to them, itching to get it off their shelf ASAP. As soon as they get the part in, your unit will jump to the head of the line.
And again, this is based off of experience of mine from before I came to work for Asus, and the basic logical assumption that there isn't too much variance in the way any given large scale computer repair operation will be set up.
