Here are some packages I want to see.
- Boost (broken into individual pieces, not a mega-package)
- gmp (although non GPL projects have a hard time using it)
More generically, things like this
- command-line processing
- unit test frameworks
- every crypto algorithm
- database interfaces
- low-level network stacks besides just Boost.ASIO
- web frameworks
- graphics libraries
- embedded languages: lua, python, etc
Also, a decent fraction of the Standard C++ library might be better off as packages, at least in the proposed drastically expanded version that includes game and UI libraries. Specifically, Boost should be available as packages, not as a machine-level installable thing.
I also expect there to be platform-specific packages. But that would be fairly rare, instead we’d have packages that had inside them platform-specific bits, but the user doesn’t care as long as it works. E.g. networking frameworks need to be built on top of platform-specific bits.