The command line program dcraw can almost do what you want. It does two things differently, though: it averages in both green pixels, and it also adjusts the color balance using its own internal algorithms. But, if you run it as dcraw -h -T, you get a TIFF file with just averaging and no interpolation — half-scale in both dimensions, so ¼ the overall area.

Here is the 1:1 pixel center crop from a random image from my working directory:

(Apologies for the non-level horizon — I was on a boat.)

Here's the same image using AHD interpolation, dcraw -q 3, and the scaled down by half without further interpolation:

Neither of these have any sharpening applied; feel free to try it. If you do, you'll find that if anything sharpening makes the AHD image's benefit even more clear. (As, for that matter, scaling it down with a less lossy approach.)

If you really want, it would surely be trivial to modify dcraw to skip the other green pixels, but I don't see any particular benefit.

For further reference, here's a conversion with Rawtherapee and its default "AMaZE" demosaicking algorithm, also resized to half-scale but this time with Lanczos resampling and with post-scaling sharpening added (which I may have overdone a bit looking now, but this is just meant to be a quick demo).

And as a final comparison, here's the out-of-camera JPEG (this is from a Pentax K-5ii):

(Resized and sharpened with a very quick unsharp mask, and then saved as PNG to avoid recompression artifacts.)