this is not a new model, hosting companies have been doing this for the last 12 years, 1&1 are not pioneering this, its just a marketing trick to get the people hosting with you who have no idea on their traffic usage so just want "unlimited" in reality they use 100mb a month of transfer and have 200meg of files (mostly e-mail)
This is the general rule of thumb - people use 30% of what they buy in large quoted plans, this is mainly due to poor space management on their behalf because they have so much space.
When people start overusing this unlimited plan will be thrown out of the window and they will be quietly removed, and because 1&1 technical support is so removed from being able to make any decision or assist in any way you'll just have to move out to a new company.
Shared hosting isn't dead, Rackspace just don't understand it properly, there will always be a middle ground of people who do not want to be contrained into a system that limits you or that is overly complex to get the same benifits you can from shared hosting for $4 a month.
Hosting companies will constantly adapt and change their portfolio to respond to their customers demands.
Saying shared hosting is "dead" is also placing the coffin lid on all the 3rd party web applications people use on their hosting services (cpanel/vbulletin/kayako). This is nonsense, people will always want diversification.
Shared hosting in effect is cloud hosting, you upload your data to servers that you don't control and you have no idea who is accessing your data at a sysadmin level or where your data actually sits. You have to have faith in the company you choose to be responsible.