For the early calls of more oversight and regulation, I don't think a dang thing is needed.
Diving a couple of miles under the ocean is inherently extremely dangerous and its up to the individual explorers to properly prepare and pay for their trip. James Cameron does it one way, OceanGate had a different approach.
This is not a ride at EPCOT. This is not a commercial SCUBA outfit in the Florida Keys. For these adventurers they knowing took risks that were clearly advised to them, including what I would assume to be numerous meetings and copious time with the OceanGate crew and employees.
At some point, the participants have to accept full responsibility for their activity. Regulations and oversight stifle innovation and creativity. Failures such as this inform others on the right... and wrong approach to dangerous exploration.