Seems so simple. Even a nip-51 list of addresses could do.

That could be easily solved by modifying the lud16 to specify a list of addresses.

This could be an option, then we can have different labels for different methods, lets say lud16, bolt12, cashureq, btc, all of these are arrays that clients can iterate on to find a working payment option.

Yes, but I think a it should consider different options, not just lightning, so you create different list for every payment method? I remember @OceanSlim porpusing something using "w" tags in type 0, it was an interesting approach, but couldn't find the related conversation, maybe he can share some thoughts on this.