I did a little googling on DirectX 10, and found this:
Games often use polygons with transparent portions (alpha textures) to representcomplex geometry such as leaves, chain-linked fences, and railings. Unfortunately when alpha textures are rendered, the intersection between the opaque and transparent portions show heavy aliasing. Alpha blending can solve this problem, but requires that polygons be sorted and rendered in back-to-front order. This is currently infeasible to do without a large performance penalty.
DirectX 10 includes support for a technique called alpha to coverage. Using this scheme, partially transparent alpha values are resolved using multisample antialiasing. This gives the transition a smooth, antialiased edge without the performance penalty of alpha blending. Outdoor games with heavy use of foliage will benefit greatly from this feature.
http://static.tigerdirect.com/pdf/NVIDIA_Microsoft_DirectX-10_Technical_Brief.pdfSounds like a version of alpha-rejection with a anti-alias style filter used on the edges to give a smooth appearance.
With this technique, you'd be able to achieve the visual quality of a tree with alpha-blended transparent leaves, but with no need to z-sort.
But if I understand the technique correctly, this does
not solve all alpha sorting issues, but it can solve a large majority of the problems associated with alpha blending. It does this not by "solving" the alpha-sorting issue, but by approaching the problem in a different way.