Landsat is basically intended for science about seasonal/annual/decade-scale changes in Earth’s land surface. When you see an estimate of how a city’s built-up area has grown since 1980, or how the Everglades are changing, it probably has Landsat as one source. This explains a lot of design decisions that might seem weird to a layperson who wants to use it for everyday RGB imagery. Most use of Landsat imagery is basically off-label. It’s just very good data in terms of accuracy, precision, and general ease of use. And if I say so myself, it looks real pretty: https://www.mapbox.com/blog/landsat-live-live/
From what I’ve seen – and I haven’t tested it carefully yet, so I could be wrong – the more elaborate methods are severe overkill on Landsat 8. It has only 4 pan px per multi px (where some commercial data has 9 or 16), and the pan band is almost exactly R+G+B (without NIR). So my gut and some simple experiments suggest that doing PCA-or-whatever is overthinking it.
> Pansharpened Malibu, 15 m (50 ft) per pixel. Notice the wave texture in the water.
Ugh, Brovey. There's better options available. Like MMP (really low spectral distortion but can be slow): http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6677587) or even affinity/guided filtering (my own paper, more spectral distortion than MMP but a lot faster and you can sharpen hyperspectral with multispectral or RGB): http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=7008094.