Although it wasn't supported, MS did allow multiple certs to be bound to multiple sites on the same IP. The problem was that it usually broke when requests came in.
In IIS 8.5 with the addition of SNI support, you are correct in that it will allow you to do what you are wanting to do now; that is, use a single IP (or many) and bind multiple sites with either a regular SSL or a wildcard.
See here for how to use SNI and wildcards in IIS. (Multiple Certificates using SNI.)
Please note, you will have to tweak some settings, more DNS than IIS, but it will work. See here for how to do a workaround.