I think this all depends on how much more power the next gen's most powerful console has over current generation systems. WiiU will not be much more expensive to develop on, yah you need to use the tablet but that shouldn't cost way to much. Nex-Box will likely be slightly more powerful then WiiU but not likely a generational leap like last gen. If PS4 is also slightly more powerful then WiiU then cost of development won't be much higher.
However THQ already stated that if next generation consoles were a true generational leap like we saw with GameCube from 64 or PS3 from PS2, then we should expect a big budget game to retail around 100$ in order for the game to break even. Other publishers have suggested a true next generation game could cost between 20-30 million dollars to make.
Fact is their are a lot of factors that would make a game more expensive, including the ones you mentioned. Face it making a PS3 game can cost millions more then a 360 title. So if you were to jump ahead an actual generational leap then yes development will be drastically more expensive.
-JC7
"In God We Trust - In Games We Play " - Joel Reimer







