I think web browsers are the big holdout for PCX support.
There is a specific reason why web browsers support what they do. If only one web browser supports something (eg APNG, MNG), and nobody else does, the feature gets dropped.
Originally web browsers only supported JPG and GIF. The former was lossy and everything looked like garbage at 640x480 anyway. GIF was lossless, and could be animated, but was limited to 256 colors. There was no happy medium of lossless, non-animated, not patent-encumbered, true-color images. So PNG support eventually wound up in web browsers, but because MSIE didn't support the transparancy, nobody supported the transparency for a really long time.
Then comes google with it's microsoft-like attitude. WebP for everyone. What does WebP do? Nothing that JPG or PNG couldn't do, and by default it's more like JPEG. Go ahead and try to find libwebpdecoder by itself. Unlike PNG and GIF, it is threaded, and unlike JPG it can do lossless and some gif-like animation.
So what do you all think newbies are going to try and do with it? Yes, they will try to render animations to webp and use those as sprites in their HTML5 games. Bad idea. Unlike MNG, which was closer to a container for "muiltiple images" perfectly suitable for sprites, webp is just webm scaled back. So if you want to loop the same 2 seconds of video, that's exactly what you'll get. I've seen this kind of thing before back in some early 2D SNES-like RPG maker software, and also later with adventure game studio. The result is not good, and brings beefy desktops to a crawl because everything is being done in software on the CPU.
In the context of the SNES, at best you can get away with RLE without a performance impairment. If you want to get fancy you can do some lz compression of text and some kinds of bitmaps, but it comes with more loading time penalties.
Audio is an even worse monster. The SNES's APU is it's own separate cpu. So you're kinda at the whim of what the SPC700 can support, so when someone goes "gee I want to play that mp3/aac/flac/wav file" you can't just upload it and play it. The web browser's do not have any standard audio file or music file support. In the RPG Maker community, the latest MV version creates HTML5 games, but if you want to make a version that works on everything, you need to export the audio twice, once as mp3 and once as aac. You know what users of that software have a problem doing? Making sounds smaller so that the browser doesn't take 20 seconds to download, decompress and store in memory.
So yeah, web browsers are a holdout, but they are also the most sloppy things to code anything for. Look at it this way.
A web browser takes 1GB of ram, supports 95% of the stuff people want to do, but does all of it rather poorly. The web browser is trying to be the new "OS" layer.
If it feels like computers keep getting faster but software keeps getting slower, that is in fact what is happening. Throw cloud computing on top for yet another entire machine fabric's worth of abstraction.