Dose Ubuntu have any plans in future to integrate a mail client independent address and calendar program?
No such plans exist. If you would like a recommendation on an address book that'll work with the panel applet and a calendar that'll work with the clock applet without forcing you to setup Evolution mail, look at contacts and dates
Nowadays when corporations and "intelligence" agencies intercept our daily communication which is all based to a consitent PIM (Personal Information Management) GNU/Linux OS still cannot provide easy-to-use calendar and addressbook solution.
Meanwhile Apple ceases to provide local synchronisation capability in OS X 10.9 and argues user should just store their data in the cloud. - Well if we want to offer people who want to switch to a free operation system they should get an easy to use option.
Imagine you are using thunderbird and want to sync your calendar and addressbooks to a CalDAV/CardDAV server (on your NAS at home or your hosting provider), such as Owncloud or DAViCal you'd need to install SoGo-connector and on top of that Lightning and hope that all would work. Still your addresses & contacts would not be integrated in your systems calender and your appointment would only appear if your mail-client is running. - How tricky!
Many other client applications have been either discontinued or ceased developpment.
Therefore I come to the conclusion that the most simple and broadly GNU/Linux compatible solution is using mutt with pycarddav and khal. - There is nothing better than the good old command line! And the most reliable solution too!
But I guess the maintainers of GNU/Linux Debian & GNU/Linux Ubuntu should finally think about ways offering working gui solutions for all these users that will switch from proprietary desktop to GNU/Linux!