The Linux CVE database was recently analyzed and it was determined that 96% of the vulnerabilities would be mitigated to at least non-critical status, if not completely eliminated, if linux were a microkernel architecture. Now throw in capabilities oriented security, and most of non-critical exploits become non-exploits. Throw in formal verification of the kernel, and you've basically eliminated everything except for hardware exploits.
Assuming mass adoption, what seL4 effectively does is turn million dollar black market zero days into billion dollar zero days...possibly more. A million dollar exploit probably isn't even a line-item in the FBI budget. A billion dollar exploit would be a "needs-congressional-approval" type of line-item in the national US intelligence budget. Unless your job revolves around protecting the nuclear arsenal of a major nation-state, you won't ever have to worry about OS vulnerabilities, and you can rely on the security characteristics of the OS to drastically narrow down your attack surface.
To me, that is a pretty big deal. It is slowly becoming a moral imperative that we start adopting this sort of security as a core standard.