Inbox for Gmail which was acquired from Timeful is a great concept.
Google won't offer it as their only web mail solution.
Microsoft won't replace the way Outlook for the desktop works.
SmarterMail can't replace how we provide Webmail.
New concepts and methods to work in mail usually get about 10% adoption right off that bat. Over the years that percentage starts to increase if that company sticks around or in Google's case keeps the project going.
What we plan to do, is continue to improve our Webmail interface. We intend to make it faster, lighter and more functional. We intend to make it more intelligent as we index more of the email messages so we can provide more proactive information etc. But we can't completely change the experience of MAIL!
At SmarterTools, we have a different vision of Email, Facebook, Twitter and overall communication. We are on the fence about trying to develop a client for Windows, OS X that not only works with SmarterMail but other mail servers as well. We believe there is a better way to work but this wouldn't something people HAD to use but could choose to use.
If you have specific features that you would like to see evolve in Webmail, please create a thread for EACH feature so we can discuss and pick the most popular of the suggestions.