It wasn't THAT long ago. Apple rolled out Intel support and Intel hardware all in 2006 for the most part, and iirc PowerPC support pretty much ended by 2008. For comparison, the original iPhone launched in 2007, the cd-drive-less MBA launched in 2008 and most Macs had no disc drives within 4 years after that.
My point is, in 2006, there was a mountain of free or open source software available online already. It was just like you said, compiled and stored in an online repository such as sourceforge or others. I remember it seemed like overnight the amount of free and open source third-party software for OS X went from barely any to hundreds and then to thousands of apps available. Everything from chat apps, disc image utilities, text editors, image editors, and more. It was awesome.
I fear a lot of that will go away with ARM Macs. For example, they don't have an official ARM version of GIMP - not for iOS, not for Android, not for Windows on ARM. It might be ported if Macs to go ARM maybe. But I can just as easily be convinced that they would sit out the first year or two and wait to see how adoption goes.
I also especially fear that Apple would use the switch to ARM macs as an opportunity to fully lock down macOS like iOS is - meaning the App Store is will be the only way to install applications and there won't be any way to download and install developer-distributed apps.