Since support for XP is ending soon, and because IE on XP was the
only realistic platform that fails to send SNI alongside its web
requests, we can assume that SNI is everywhere. Or at least, that is a
safe assumption from April 8th, 2014 -- when IE on XP is officially
acknowledged by its source as an insecure browser. (Others have said the
same thing for much longer already.) So it is not unlogical to stop
supporting browsers without SNI.
TLS servers often struggle with a limited amount of ports. Even when
using IPv6 there may be reasons why this problems shows up; backward
compatibility with IPv4 and a desire for central entrance of web traffic
to your site are a few. SNItch makes it possible to switch to various
backend servers based on the Server Name Indication contained in (at
least) web traffic.