you know if you upload that library to iCloud music library FOR FREE then HomePod will be able to play it using voice command ???
1. My iCloud is 5GB. That would fit a thumbnail of my music.
2. According to Apple's HomePod web page tech specs:
"Apple Music subscription for full music functionality"
With footnote:
"Siri works with Apple Music. Subscription required for Apple Music."
So, no, your solution would not work even if I did want to pay for iCloud storage. But to clarify my point for you, Siri will not play my personal library on my personal drives.