Is there any way to set a dashboard as "Home Dashboard" for all users...?
I mean something equivalent to,
user-prefs.conf
[general]
eai_app_only = False
eai_results_per_page = 25
display.page.home.dashboardId = /servicesNS/-/my_app/data/ui/views/my_dashboards
that applies for all users
there is a similar question with a good answer
https://answers.splunk.com/answers/204452/change-user-default-home-dashboard.html
If you want to setup a Home Dashboard for your Splunk Instance, you can try the following option: https://docs.splunk.com/Documentation/Splunk/latest/Search/NavigatingSplunkWeb#Home_dashboard
If for a specific Splunk App you want to set a default dashboard to be loaded when App is selected, you should set default="true" against the Dashboard which should load as default dashboard in default.xml for Splunk App's Naviagtion i.e. from Settings > User interface > Navigation menus. By default the default option shows search.
Refer to Dev Site Example for default home page for App: http://dev.splunk.com/view/SP-CAAAEP9#default
Special Thanks for taking time to respond.
This can add a default dashboard.
But What I want is to set a default dashboard in splunk launcher app's (or my custom launcher app's) home page.
I mean when the default.xml is like below
<nav>
<view name="home" default="true" />
</nav>
Please refer the screen image

In your screenshot, if you choose a Home Dashboard, when you Launch Splunk, that Dashboard will be displayed.
If you want some dashboard to be displayed by default when you click on an App like Hello World!, you can set a default dashboard(view) to be displayed using the xml you have posted. Instead of home, you should use Dashboard Name (PS: If you navigate to Settings > User Interface > Views it is View Name). Or else when you open a specific dashboard the view name is part of the url after the app name.
If you need something other than this then you might have to add a mock up of what you need.