The Daytona hollow mast could be a promising solution for a big efoil company (Flite, Lift, …) but IMHO inappropriate for DiYers or small companies.
Here is a trade-off: the mast extension for ESC that can receive a compact ESC (@nickw1881, or a 120Acont 81x31x17mm MGM compro. The idea comes from the kitefoiling scene, costs 200 to 300€ in carbon (Groove, Ketos, …), 100+ usd in aluminium like Mantafoils or GoFoil. Here is the KETOS carbon one.
This efoil mast extension needs to be hollow, an ESC space must be easily waterproofed with a top and bottom joint, DiYed or CNCed from aluminium (like Mantafoils, GoFoil, …). The outside must be streamlined but the inside on the plate side can have a rectangular custom shape to match the ESC case.
This ESC mast extension could also be molded in aluminium around the mast airfoil section, see @Beninspain method using lost PLA (I am looking forward to watch you video casting a motor pod )