Sadly support for SNI isn't supported widely enough that you can actually use it, unless you control the clients.
You really need Internet Explorer to support SNI on Windows XP before you can use it. We would lose maybe $50- 100.000 in turnover per month by relying on SNI support, rather than just having multiple IP for each domain.
If a browser doesn't support SNI, it doesn't prevent them from accessing the site. It just means the wrong cert is returned, so they get a cert warning. Depending on the type of your site and type of users, this may or may not be a problem.
Windows XP is completely and utterly deprecated as of next month. For any future deployment and new development it should not even be on your consideration-matrix.
It's dead, Jim.
Let's just let it die already, instead of sowing cushions under XP-users arms. If their internets starts breaking, they might actually be motivated to upgrade.
You really need Internet Explorer to support SNI on Windows XP before you can use it. We would lose maybe $50- 100.000 in turnover per month by relying on SNI support, rather than just having multiple IP for each domain.