My formula would be to give players 80 minutes for the first 40 moves, then 40 extra minutes for the next 20 moves, and then 30 more minutes for the rest of the game if the game goes on after move 60. And there should be a time delay but not an increment.
So this adds up to 5 - 5.5 hours max. Realistically, most games probably won't even last that long. They will be easier to watch and the high quality of classical chess will still be present, in my opinion.
Another point I'd like to make is that in a longer game, it's not only the viewers but the players themselves get tired and tend to make more mistakes. Evidence of that is yesterday's game between Fabiano Caruana and Ding Liren. Players were really tired. Admittedly, there was a time trouble factor too, but some players always get in time trouble.
And of course, I'd like to emphasize this point again, shorter time controls will add to popularization of the game. For many amateurs, playing long games in tourneys may be a bit too much. Older players will have a better chance too since they will need to concentrate 5 hours instead of 7-8. And, what's also important, this slight change won't affect the quality of classical chess too much (as opposed to shortening time controls too drastically). This solution may be a compromise standard for the 21st century.
It is important to understand the needs of this century and that things need to speed up at least a bit to stay relevant. People's time is valuable and they are the consumers whose desires and time need to be taken into account as well. More viewers translates into more ad time and more money for the sport.
I think I've made my points and repeated myself a few times while at it. 
Here's the link to Caruana - Liren game press conference.
https://www.youtube.com/watch?v=HNRC5NDeN-g
And of course, I'd like to emphasize this point again, shorter time controls will add to popularization of the game. For many amateurs, playing long games in tourneys may be a bit too much. Older players will have a better chance too since they will need to concentrate 5 hours instead of 7-8. And, what's also important, this slight change won't affect the quality of classical chess too much (as opposed to shortening time controls too drastically). This solution may be a compromise standard for the 21st century.
It is important to understand the needs of this century and that things need to speed up at least a bit to stay relevant. People's time is valuable and they are the consumers whose desires and time need to be taken into account as well. More viewers translates into more ad time and more money for the sport.
I think I've made my points and repeated myself a few times while at it.
True, but usually class players don’t play GM time controls, even in classical tournament games. The standard 90 30 or G/120 d5 seems fine to me.
Hola People!
Who has been watching the Candidates' Tourney recently? I have been. And I must say, I did enjoy watching chess. However, I've always thought that these chess games are way too long. Granted, before I thought that time controls should be even faster, but now my idea is that perhaps they should be a bit faster but not too much. In other words, games should last 5-5.5 hours max instead of 7-8 or more hours.