I’m not. And I’m just throwing around ideas here. I don’t think it’s outlandish to agree on common formats among different clients/languages, and I don’t think there’s a lot of overhead in updating 2 files for a simple change of e.g. a contact. That might be a different story for other modules, but that’s why every scope/module/data format should be solved using case-by-case solutions imo.
For contacts and calendar entries it just makes sense to use formats that we can directly drop in to all existing programs that support it. But we could also store transformations of those formats in JSON-LD, which is more suitable for the Web, so that unhosted Web apps don’t have to jump through lots of extra hoops to be compatible to “legacy” standards.
I don’t think contact and calendar data is big enough to call a duplication “massive” by today’s storage and bandwidth standards.