While PlexAmp was in heavy development I (and others) asked Elan specifically about this and was told there is no intention of adding an EQ as that should be part of your hardware and not the software (or something like that).
If there isn’t any interest in adding an EQ to a dedicated music app then I doubt we’ll ever see it in the web or other client.
Ripped music (in general) is far worse then playing CDs, albums, cassettes or even 8-track (gasp) if you ask me. When people rip music they use a lot of different software and end up with different ranges of volume. By this I mean when CDs are mastered you can usually pick 12 CDs from your library and get pretty consistent output levels if they were mastered correctly. Once end users start mucking with them and use tons of consumer tools on them the output can be all over the board making the use of EQ that much harder.
Once of the reasons I’ve never been a fan of Plex music in general is the lack of dynamic normalizing that helps to fix much of this. The music really needs to be normalized before worrying about an EQ.
With that said I’d love to see EQ profiles and not just one setting. I might be using a set of ear buds that need one setting, an expensive set of headphones with another setting and maybe BT to the car or home system that each could use it’s own setting. Put another way the ability to setup an EQ profile for the output device being used at that moment in time!
There are a bunch of freeware/open source EQ programs/libraries on the net that might be able to be leverages so hopefully someday we might see something like this added.