QSYSMSG is viable at least through i 7.1 with no indication that it will ever not be viable. Many of the messages that the system sends to QSYSMSG are duplicated in QSYSOPR. Some messages are sent to both message queues. There are messages that will only be sent to QSYSMSG when the related SRC is appropriate.
New technology is kind of irrelevant. QSYSMSG exists in order to avoid lock conflicts with QSYSOPR and to provide a less cluttered view of the critical system messages that may be sent. Some of the messages that the system may send are caused by hardware failures that new technology will be unlikely to work around.
For example, technology has some trouble with CPF510E, “Network interface &9 failed while doing a read or write to device &4.” Or CPF5342, “Line &9 failed on device description &4, remote location &5.” When network interfaces or communications lines are failing, it can be tough sending anything anywhere outside of the system.