I don't think Apple wants to use proprietary connectors. In the past, they have fully embraced standard connectors, when those connectors were good enough. They ditched ADB when USB came out, and they ditched FireWire when USB got fast enough to transfer video.
What they won't do is use a standard connector if they feel that all standard options are compromises. When they felt the need to move away from the 30 pin iPod connector, they felt that the USB options were insufficient (not fast enough, not enough power for charging tablets, and most importantly, not reversible), so they developed Lightning to solve those shortcomings. I think if USB-C had existed at the time, Lightning might never have been developed.