M series is consumer stuff, mostly non weather sealed. Not sure whether it can be used in extreme wet condition? Cameras like 7D, 5D series are weather sealed and I don’t have any issues using this in outdoor plus wet condition. these cameras doesn’t require hot shoe covers. The R3 should be similar or better than these cameras in terms of ruggedness i.e mainly weather sealing. But if the hot shoe requires cover to meet the requirement is a little concerning. It’ll be a single point failure if the user forgot to insert the cover prior use in wet conditions. It’s now in similar state as Sony high end stuff.The M5 came with a hotshoe cover but didn’t require it. Which rather disproves your thinking.