Just read about another deep diving submersible, now owned by Gabe Newell (as of last year), it holds the world records for deepest dives across the five oceans and is the only submersible certified for unlimited ocean diving. Quite the fascinating read and it looks rather badass too.
en.wikipedia.org
And the name is rather cool too
'DSV Limiting Factor'.
The records were broken by the previous owner, Victor Vescovo, before Gaben bought the company though. Still, the team still operate and dive to such depths, because the vehicle is fully rated to far beyond the deepest known depths for depth-unlimited diving.
Edit*
So yeah, if you follow the right paths in regulations, certifications and focus on engineering expertise, you can have a safe diving vehicle with depth-unlimited capabilities anywhere on Earth.