I think that's effectively already the world we live in. As a uBlock user I occasionally run into sites that are broken because they wrote code assuming that some function provided by an analytics library would exist, and it doesn't because that library got blocked. I file bug reports when I can, and I'm concientous about handling these cases in my own code.
Writing code to handle the failure to load of third party scripts like this should really be a best practice anyway. Even if you use subresource integrity checks on all the external scripts you load, what if some analytics provider's site is down for a while? Do you want your site to still work? I do. (Obviously this does not apply to scripts that are actually necessary for the core functionality of your site, but that doesn't really apply to analytics/tracking tools for the most part.)
Making this the default behavior of FF will make this sort of breakage more visible to more people, it's true. If anything maybe this will encourage sites to write their code to handle failure more elegantly and I'll spend less time annoyed. One can dream.