The new model of One Version, all updated together is interesting in this context. Examples are iOS, Chrome, Firefox and node_modules. All super complicated with many dependancies. Update everything, fix broken stuff. Only maintain the one blessed dependency graph.

If you report an iOS or Chrome bug where you tried to revert a library upgrade and something broke, they'll just mark it "Won't fix: omg never ever look at this".

The dependency graph when everyone isn't updating all at once is brutal. Half of Unix life is/was "well I need to update X, but can't because Y depends on old X. Now we'll just create this special environment/virtualenv/visor/vm with exactly the brittle dependency graph we need and then update it, um, never."

We complain about One Version/Evergreen, and should, but it's got huge advantages. And might be an indicator that testing surface is the real complexity constraint.

One Version's success a good indication that Plan 9 was at least not totally wrong.