> For most people out there router is this thing connected to cable modem. Even if it's technically not router, but firewall with NAT.
<pedantic>Every NAT or firewall is technically some kind of router</pedantic>
More generally speaking,
I do not think any core network device blocks SCTP (nor anything else they do not recognize). So if two parties want to SCTP, they can by just reconfiguring their edge devices. Except for NATs, but NATs will disappear with the very near exhaustion of IPv4 addresses and the pressure of P2P applications.
You do not need the whole planet to be able to use a new protocol or service in order for it to get some traction. Zillions of people are forbidden to use facebook (and others...) at work. Does that dooms facebook?