So, apologies for being a bit cynical here, but I don't see this one being addressed any time soon.
it's been at least 5 years since npm started getting scrutiny relating to security weaknesses https://blog.andyet.com/2012/03/08/compromising-the-integrit...
and 4 years since Rubygems was compromised http://blog.rubygems.org/2013/01/31/data-verification.html
and yet, I don't see substantial movements relating to package security and trustability in these repo's. To be clear I'm not suggesting these two are any worse than others, they're just large repo's who have had incidents in the past.
The problem here (to my view) is that increasing the security of package repo's will slow down releases (additional checks take time) and cost money (additional security, hosting etc) and until there's a market demand for those service, they won't happen.