Short-term it may look like there's less freedom since it's harder to use M:N threading (and 1:1 threading and M:N threading don't necessarily work perfectly to

Short-term it may look like there's less freedom since it's harder to use M:N threading (and 1:1 threading and M:N threading don't necessarily work perfectly together), but remember that the choice there is 1:1 threading with overhead and M:N threading with overhead. Long term, we can have libraries that provide M:N threading with minimal overhead; and also libraries that provide 1:1 & M:N together like the old std (with the associated overhead). That is, the programmer is getting more flexibility, just not right now (especially with Cargo, which makes it particularly easy to use external libraries). The team is trying to take a longer term view focusing std on safe interfaces to the OS primitives, which can then be used to build fancier/more abstract libraries more easily.