This will be offered soon. We will update this when we’re closer to releasing this feature.
Collaborative lists are partially implemented, just not live yet. Friends are also partially implemented. Both of these features will be released once they’re tested and ready. Thanks for the suggestion!
I’ll do you one better, the planned functionality is to automatically sync achievements across Steam, Microsoft, and Sony systems using their services. I haven’t looked but it may be possible to take in achievements from GiantBomb too, which would provide an “official” way to add achievements to games that don’t expose any.