Both United Airlines as well as American Airlines have introduced or are introducing "new" basic economy fares. These fares mean that seats are allocated at boarding and those travelling together may not be seated together, passengers are limited to one light carry-on item only (in the case of American Airlines, this means no access to the overhead bins) and no changes are permitted on the fares; not even upgrades. Passengers paying the really basic fare are also the very last to board. That said, I think it will be hard for the Flight Attendants to police the use of overhead bins - especially when the flight is not very full, where such action could only be described, at best, as churlish. I can see such restrictions resulting in many a case of (really rather justified) anger.
You still get free soft drinks, snacks (such as they are) and access to the in-flight entertainment.
This time, at least, there is no question of the marketing types saying: ".... you told us".
There are now three sorts of economy fares: Economy Plus, Standard Economy and now, "basic" or as far as AA are concerned, Main Cabin Extra, Main Cabin and Basic. The fare savings make one wonder, however, if it is worth it. One way Dallas Forth Worth to Philadelphia on the 4th March on AA will cost £117.80 on the very basic fare. The "Main Cabin" fare is £123.20 and one wonders if being last on and not being able to use the overhead bin is worth the £5.40 saving.
You also need to watch even more carefully what you are buying as most systems default to the cheaper fare which, to my mind, is not that sensible. Better would be to quote the "standard" fare and then offer the basic fare as a saving, should you not mind the indignity of having to take the walk of shame (as you get on last and have to go to the back) and then have to struggle to find somewhere to put anything.
To my mind, however, airlines are coming at this from the wrong angle. Rather than asking "What can we further remove?" They should, perhaps, be asking "What options could we add that will materially benefit the comfort of passengers?" If you are paying, say, £130 for something, would you prefer to be forced to pay an extra £5.40 for something that was previously included; or would you prefer the option of paying £15 or £20 for something that materially benefits your comfort?
For example, one could take a number of rows, anywhere in the cabin (say, at the back) and give those rows an extra few inches of legroom or marginally wider seats. I have not worked out the mechanics of how such a move would pan out from an airline costing perspective - but the idea is that one offers something more, that really benefits the lower fare passengers, rather than trying to squeeze out their last few cents for something which is more an irritation-removal, than an actual benefit.