We'll try to give site operators a configurable choice of multiple solutions -- certificates with multiple Subject Alternative Names (SANs); per-site certificates deployed using Server Name Indication (SNI); IPv4 addresses per site if you have enough; or IPv6 addresses per site.
All of these solutions have different problems and limitations:
- If mutliple-SAN certs get too large, they cause performance problems, and some clients may not be able to handle them
- SNI isn't supported by Safari and older IE on Windows XP, or more alarmingly by Android below 4.x
- IPv4 addresses are scarce and costly
- Many clients still can't route IPv6
Sophisticated hosting platforms may want to use all of these methods in combination.