Oxe has a 300 coming. I believe it's BMW based. Only seen some prototype shots. It was on a boat running quads.
The diesel market will never compete with high performance boats IMO. Fuel economy is better of course, but the lack pf RPM translates to lower top speeds. They are more suited for heavy boats. These generally are not top speed targeted.
But, if an owner ran a boat enough hours, the maintenance and fuel savings should break over by 3000 hours. And the extended life of the diesel should also play a role here too. There is lots of interest in the Miami and Bahamas regions. Lots of long runs in open water. For fishermen, fuel costs are a big deal. Even for those spending $300K+ on a new boat. Being able to fuel in Miami and make it back without a stop is a big deal I guess.