It's somewhat funny that all Carnival Corp. companies, Carnival, HAL and Princess all made the announcement the same time.
On my last couple of cruises on HAL the casino was designated non-smoking on formal nights. On those nights the casinos were very quiet.
It will be interesting to see how the change in policy affects the various lines. HAL for example, never has a very active night life, so the affect there may be minimal. A bit of a similar situation with Princess.
Carnival MAY find that their bars are busier without smoke floating around. The reaction should be easily and quickly ascertained.
Carnival Corp. obviously believes they can alienate 20% of their customer base, and replace them by attracting a larger segment of the remaining 80%.
Personally, I think NCL has it right. Smoking allowed in cabins and on balconcies, with the remainder of the ship (indoors) with the exception of the casino designated totally non-smoking, and restricted outdoor areas for smokers. (However though I haven't sailed her, I guess the design of the Epic's casino allows smoke to spread throughout too many public areas).
Being in the 20% group, we'll have to wait and see how these changes affect my cruising choices.