Let me chime in here real quick.
My understanding of the 24 hour limitation is that it was a multifaceted product and engineering trade-off. The two key reasons were:
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The simplicity of the current system results in a robust, pretty much bulletproof download system. On the other hand, it doesn’t scale up to very large libraries well. The limit is there to avoid performance issues and potential breakage.
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From a product angle, Plexamp is designed to work best hand-in-hand with the smarts of the server. All the radios, mixes, sonic similarity, advanced metadata, smart shuffle etc. that make Plexamp such a great, unique player require server features that would be near-impossible to implement for locally downloaded media.
Given the above design goals of a simple, robust, unique music player, a fancier and inherently more complex download system was considered out of scope for the initial release of Plexamp.
That said, Plexamp’s developers have heard the community’s feedback, and have said a few times in the past that the download system is something they’re interested in revisiting for a future release.
Given that it would involve a significant rethink of how downloads currently operate, it will take time to get right, and unfortunately isn’t as simple as just “removing the restriction”.
I hope I’ve provided some clarity here, and allayed any fears that we’re not listening to feedback 
