Download the repository for 11.4 beta on oracle site.
Create a local repository on the machine in question (this will require couple of GB).
Using pkg command, set the publisher to point local repository.
Create a backup boot environment via beadm, which you will revert to if things do not work.
Even tho system update will probably create boot environment automatically i like this clean and named as i want
Try to update via
pkg update --accept from the local repository.
This should update your system from 11.3 to 11.4
Often update from major to major release do state you need some SRU before, but i have tested several upgrades without issues between major releases.
Perhaps those are some borderline cases, but pkg update should fail in that case, leaving you with working environment due to the way solaris is patched.
Hope that helps
Regards
Peasant.