In reply to Peter Knight.

But somewhere down the road it is going to be rather nice to be able to code without having to install separate tools on a machine. There would need to be some sandboxing functionality to prevent against crashes and the like, but it’s a worthy long term goal

No it's not. No professional developer codes on the live site. If someone does, they're internalizing bad practices and WP should not encourage those.

The bottom line is that altering code on a live site simply is never good practice. In rare instances it might be necessary to fix a crashing, site disabling bug. But developers should always, absent those circumstances, code on a development installation and move those changes to live once tested.