Are there any plans to introduce support for SNI and not requiring to have separate IPv4/per domain for SSL certificate?
Yes, there are.
And… it's done. You can now add Secure Hosting to a domain at DreamHost without a Unique IP.
Note that there are some caveats: the technology used to enable this feature, SNI, is not supported by some older browsers. See http://wiki.dreamhost.com/Unique_IP for details.
In my humble opinion, this has been one of the most welcomed changes I've seen in recent years from Dreamhost. Hooray!! Thank you very much!