Microsoft ‘secretly’ already supports CardDAV/CalDAV in their latest Windows Phone versions. There is a workaround to set it up:
We’re planning to support this as soon as possible. The problem is that there’s no real standard for groups yet (e.g. Apple uses a special non standard vCard for groups, Mozilla Thunderbird uses a different special vCard – none of those are standardized).
All of that will luckily change with the vCard 4.0 standard, which we plan to support as early as possible. So once CardDAV clients support the new vCard 4.0 standard, we’ll also definitely support that, which will result in cross-platform support for groups.Ian commented
If there is no real standard, then it is an opportunity to implement a premium (paid) feature to handle the different proprietary standards. Why wait?
It would be a good way for Fruux to differentiate itself. When they all implement an open standard, then your competitors will probably offer this and then it will be difficult to charge money for it. I just signed up for a pro account and expected a little more progress on the implementation of these kinds of features, but I'm willing to stay a while and see how you get on.
Other potential "premium" features could include things like what the "Humin" app tries to do: help with convenient searches by location (where did I meet this person) or by date (when).
We plan to provide such functionality in the future.
In the meantime: If you are using a Mac, the Addressbook application has a built-in deduplication function that could help here.