My suspicions were just confirmed. It's not a ZAPI issue, it's a MultiStore/vfiler issue wrt support for https. I don't have a timeframe for this support. You could open a case and make sure an RFE is filed to make sure it gets on the roadmap. And if it is already there, more customers asking for it always helps.
Re: wanna use zapi over https to communicate with a vfiler