19 years is a great run. Was an amazing console with a great library, and basically set the standard for controller design. Rock Band is probably the community most affected by this, but I think most of the songs are available via a hacked console anyway.
Honestly I find it amazing just how long the 360 has gone without a viable modern softmod. There was one singular one found on a firmware so old it still has the blades dash but otherwise no modern ones are publicly known. That said, I wouldn't be surprised if one appeared almost immediately after the store was closed because the person or group who found it was waiting for just that situation before releasing it.
Just what did Microsoft get right in terms of security on the Xbox 360's software?
You get hardware banned from Xbox Live when a mod is detected, simple as. There's not much incentives for offline modding because most of the 360's library is easily moddable on PC
