Disabled elements need focus?

Dear a11y specialists,

Few of our friends are having different opinions on providing tab focus for
disabled buttons and links. When a disabled attribute is used keyboard
focus is not observed on buttons and links in some browsers. Is it the
expected behavior? One set of people argue that screen reader user will
never know that the element exist if the focus is not provided. The other
set of people argue that providing tab focus to disabled elements cause
additional frustration especially in a process where time is a major
factor. I have provide some situations where the disabled attributes can be
observed in general. Any thoughts on the topic is highly appreciated.

a. Seats that are already booked in a seat selection widget: If keyboard
focus is provided for booked seats, user should focus to all unavailable
seats. In many websites booking process should complete in 15 minutes.
Providing keyboard focus for non interactive elements will result in
delaying the ticket booking process for keyboard only users and screen
reader users.
b. In a calendar widget for selecting a birthday, all the future dates need
to be in disabled state. Do they need tab focus. Similarly for booking a
ticket previous dates will be disabled.
c. Future links in a progressbar: In a checkout process, current step will
be active and the future steps are non-interactive until reaches that step.
Is it required for the user to navigate and check the steps with tab key or
making them non-focusable is fine.

I would like to get your thoughts and publish a blog article.
Thanks for your help in advance.

-- 
Best Regards
Rakesh Paladugula
www.maxability.co.in