In Wii Sports Resort they have highest score leaderboards for certain sports like Wakeboarding, could this be implemented into the Games in Wii Music?

I don't think that score-based categories should be a thing. If you want a leaderboard for scores, take a look at Cyberscore: https://cyberscore.me.uk/game/2165

They do exist, on Wii sports resort's category extensions, as the highest and lowest score categories.

Unfortunately I don't think we'll add a high-score leaderboard as of right now, at least for here on SRC. Most High-score related leaderboards here have some important speed tech, strats, or optimizations that make it more than just grinding away points (think Starfox 64 and even WSR Wakeboarding). The only candidate in Wii Music would be Pitch perfect, but the only "speed tech" is just moving the pointer around and being correct, which is no different from the run as it is. A high-score leaderboard for ILs would fit in much better on a website like cyberscore, IMO. Sorry y'all