I think we are on the edge of a shift in digital cameras.
We need to step back and ask "why mirrors". In the days of film, you needed the mirror and optical viewfinder to know what you were looking at and we needed focusing screens to know if we were in focus.... Then came digital sensors and we treated them like film... because that is what we were used to.
A digital sensor is NOT film. It has different strengths and different weakness.... and the mirror is no longer the only way to see through the lens. A decent mirrorless camera (and there are several on them out there) will be designed to the strengths of digital technology. They already do many things better than DSLRs, but a great mirrorless camera will have to do everything better. Right now, the two big stumbling blocks are focusing and viewfinders.
Exactly, plus, for some photographers, battery life can be an issue with mirrorless cameras. Especially travel and nature photographers, who cannot easily charge batteries when they are "on tour", should consider this. Mirrorless cameras suck power for EVERYTHING. With a DSLR you can look through the OVF and check composition even when your camera is switched off. With an EVF the cameray needs to be on, all the time, and the mini tv set, called EVF, needs power.
Since my old 5D1 died I am looking around, what my next camera might be, and as I don't own a lot of expensive glass, I am open for other systems, too. While many Canon shooters go for Sony, it seems, I got even more interested in Fuji's X system. However, I found that I can get only about 300 photos with an X-M1, when I was able to take about 800+ photos with a 6D (had both for a rent for one day).
Regarding (not only) AA filters, Fuji is lighting the way. As has been said here, Moire (sorry, no diacritic characters on the keyboard I am using right now) was no problem with film, due to its amorph distribution of grain. No geometric pattern, so no interference with other geometric patterns. Simple as that. And it's exactly this, what Fuji is trying to achieve with its X-Trans sensors.
So, while I agree with most of the arguments that AA filters are useful, these arguments apply more (if not only), if the pixels on the sensor are arranged in a geometric pattern, that could interfere with a geometric pattern in the image, which is less likely with an X-Trans sensor than with a "classic" sensor, where the pixels are arranged in the Bayer pattern.
BTW, while better lenses may increase Moire, the way out, apart from other, more chaotic arrangements of senser pixels, is to increase the megapixel count. Only when they reached 24+ MP, Nikon and Sony dared to make cameras without AA filters. Why? Because, the finer the structures and the smaller the areas that can possibly cause Moire are, the less of a problem they will be in the resulting images.
Well, I am not a techie, and maybe some expert can give more detail, and maybe someone with more didactic experience can explain this a lot better than me, but I hope, I was able to give correct facts. (Otherwise, please correct me!)
Finally, for those of you who want to have AA filter or not as an option, the Pentax K-3 should be a very interesting piece of technology....