Right, based off some ideas and a mail message...

 Right now, generic components in GNOME are very very simplistic.  For
example, the E-Mail application preferred setting is just a command used to
open a new mail.  Same with a web browser.

 What would be far more powerful, and thus enhance user experience and
desktop-usability(imo, anyways, see below), would be to have a standard
GNOME component/control for these things.

 GNOME might not actually ship any implementations of these controls. 
Instead, these would be "specifications" that applications would make use of.

 As an example, for E-Mail, and app that needs to send e-mail could connect
create an instance of this component, fill in the needed headers/body, and
then call a "compose" or "deliver" message.  Compose could open up the
email editor for the user to refine the message, or deliver could just send
it.  (In that case, the component would probably open a dialog saying
"Application XYZ wants to send an e-mail to Foo.  Send Message?  [View]
[Cancel] [Send]".)

 For the web browser, it could be a comprehensive browser control.  Open a
new window on the current viewport, and send commands (open this url, open
that, etc.), but only to the window it opened.

 The methods/names/etc. of these of course need to be determined.  I
haven't the background/experience to do that properly, tho I certainly have
ideas on what they should do (if not how they do it).

 Then apps like Evolution/Balsa/Epiphany/Galeon/Bug-Buddy/GNOME-Office/etc.
can have highly integrated, cooperating features that can be swapped out
for alternative applications.  (i.e., if user prefers Evolution over Balsa,
the Evo version of the GNOME-Email component control would be loaded when
an app requested it.)

 And, for non-GNOME/legacy apps, GNOME could ship highly simplified
controls.  For the web-browser, it might just wrapper moz-remote, and for
e-mail it might just run some specified command/script.