I have a 4.3 Wii which I plan to hack using Letterbomb, will I still be able to play Skyward Sword via legit disc?
Will it ask me to update to a new firmware you think?
Hell no. I haven't seen, heard or played skyward sword, but I just pull out of my ass* that it will come with mindreading software, so that in case anyone in the room even THINKS of playing a backup of skyward sword (yes, even when "backup" is used in the literal meaning of "having an extra copy that is only to be used next to the retail game"), the wii will explode, the user's parents will be killed and anally raped. Nintendo will be notified that the warranty is void for the game, the wii, and all other nintendo games/consoles/accessoires ever produced and will produce in the upcoming 50 years. This goes for the owner of the wii, their family, roommates, relatives, friends, pets and facebook contacts. Of course it'll be cracked within a couple days, but damnit...nobody will ever say that nintendo doesn't know how to give the hackers a run for their money.
It will also have a new firmware. It will be 5.0, which will be faster, more reliable, a better experience, pack more fun and more of that "hot air"-stuff that 4.2 and 4.3 supposedly brought. It will remove all cIOS, automatically unplug any USB drives, format your SD card and requires you to fill in a 50 question enquete on why you like nintendo so much.
...the game itself will run fine on sneek.
*going by how gbatemp works, this is just as credible as any other source