[Klojum]

As this thread is a couple of years old, I wonder if any progress has been made since?

Since you posted in a 2018 thread, I'd thought it would be better to split it into a new thread.

I think Kodi is a great system for repurposing old hardware into a great media center.

That only goes so far, we will not support old hardware indefinitely.

About your hardware, the RPi-1 is basically the slowest device to run Kodi on. It was a success because of its capable video graphics chip.
All the loading/browsing of your music collection is mainly a CPU task, and your RPi-1B at times will probably need to do some catching up.

My only concern is the load time on the app

It's a RPi-1B... Try using at least a Class10 SDcard. You could also try some overclocking, but don't expect miracles.