Unless Harley had someone design a proprietary switch with a unique thread no one else in the bike or auto industry uses, which is extremely unlikely, I'm sure an adapter could be found that will screw into the engine case. It may not be the same as the Twin Cams, but that doesn't mean you can't find an adapter. Figure out what the actual thread size is, then it becomes a case of searching for an adapter. If it's metric, most of the cars on the road these days use metric so I'll bet at least one brand uses something that matches.j
Yes, the current kits that mount to the rocker cover aren't going to fit the M8. Harley may never offer a kit that fits, but I'm guessing the aftermarket will once they realize people want to know what the pressure is on the new engines. In the meantime, temporarily rigging up a mechanics gauge so you can check pressures in various riding conditions should be fairly easy. People did it for decades with Evo's and Twin Cams when diagnosing oil pressure problems, so it's not something new.
Jerry