Competitive players are also part of the fandom, dear. Like it or not.
I just agree that Sound and Light sounds silly as a new type. Light MAYBE can work then again it would be kinda weird since Psychic is already fulfilling that role already.
In any case fans are forgetting to see where it needs to be seen. Everything that doesn't fit the other categories fall under the Normal or the ??? category. So THERE IS where they should look for new types.
I would even like Magic rather than Sound or Light since it's more generic and more moves can fall into that category. Or Alien. Or whatever. But SOUND is pretty lame for a typing and Light is too much Psychic rip-off.
I can even THINK on the Pokemon it could has (Clefable line, Togepi line, Castform, Smeargle, Porygon (?), Audino, Mr Mime, Unown, Lunatone, Solrock, Chimecho, Sigiliph...And maybe Misdreavus line) and the place in the chart (Effective against Fighting, Dark and Ghost and weak to Psychic and maybe Dragon. You know, co'z Dragons are stronger in magic(??) )
Anyway, what I'm trying to prove here is that people oversees how balanced the game is and there is no need yet to implement something new because you can still construct with the ones you have already. Even if you repeat Pokemon dual types, you've almost infinite combination when it comes to moves, abilities and stats to be made and enough concepts to keep enjoying Pokemon for a long time. There is no need to insert something that would cause unbalance if doesn't bring something interesting into the table either.
Wouldn't Magic be more of a 'ripoff' of Psychic? To me, Psychic as an element is just heightened inner senses, that kinda sounds magical to me. Then again, lots of Ghost and Dark type moves sound magical too. I'd expect Light to work as a direct opposite of Dark, though like you said, there's the neutral Normal-type. Sound just sounds flimsy to me but I understand lots of people want it too.
Agree with you wholly in your last argument though. Whatever type combinations they come up with it depends on the Pokemon itself and the way it is designed.
On the discussion of bug types, yeah they pretty much got a lot of glory in Gen V (Champion in BW used 3 bugs) but do you think this generation, any other types would get the 'royal' treatment? Not saying that bugs did get the royal treatment in actuality, just to those who sorta notice it that way. Personally I think its because that Bug seems more of like a 'novelty' type as compared to the other elements, thats why their pronounced identity in Gen V was kinda noticeable.