I am still waiting for a proper browser based mail client that will let me read email from a variety of IMAP servers, rather than email 'clients' that are actually not clients, but just interfaces to a particular email service.
Relatedly, I really, really, wish ChromeOS would support smartcards but reading the frustration of the government/military types that have been begging for this feature for years with no real interest by Google is very disappointing. I really like the form factor of YubiKey Neo that simply hangs on your keychain and just sticks into a USB port to become a smartcard. We're also never going to have gpg-agent on ChromeOS so smartcards is pretty much the only way to keep the private keys off the machine.