In theory there is a way out of this dilemma, oversample. A sensor of a given area will detect the same number of photons, provided one can neglect the effect of the packing fraction of the photosites. By having a sensor with very high spatial sampling, one can increase the Nyquist frequency and eliminate aliasing. The price one pays is increasing photon noise level. But one can downsample the image, regaining signal to noise ratio at the expense of resolution. This has the advantage of being completely in the digital domain; the AA filter effect would come at much higher frequency and thus be of no concern. There could be many useful tradeoffs with this approach. By the way, this idea is very similar to the oversampling applied to digital audio recordings: The audio data are sampled at a very high rate while recording, then resampled to 44.1 KH for production of CDs.
Yes, I'm familiar with the concept of oversampling, yet I find it very curious that every time Canon increases the pixel density of its DSLRs, which all include an AA filter without exception, there's great concern on forums like this that no purpose is being served because Canon lenses, in general, are not good enough to justify the higher pixel density.
If that's the case, why the need for an AA filter?
If a top of the range 39mp digital back like the P45+, with the pixel density of the 1Ds3 and less
pixel density than the Canon 40D, does not have an AA filter, why do the latest Canon DSLRs need an AA filter?
When Sinar and Rodenstock produced their digital series lenses, there was a lot of excitement at the sheer quality of these lenses. The published MTF curves implied they were sharper than most 35mm lenses. In fact, they seemed to be similar in resolving capability to the renowned Zuiko lenses used in the Olympus 4/3rds format.
How do owners of the P45 manage with such razor sharp lenses that are almost diffraction limited at f5.6, considering the P45 does not have an AA filter?