Think they will do this in 5th ed?

[Spacehamster]

a book that covers lvl 21-30 adventuring?
Prob not in quite a while I guess since the game is still quite new?

[JumboWheat01]

I do wonder how they'll handle Epic levels. Will they raise the stat cap, or keep everyone with a limit of 20? Will we get another ASI? What abilities would we get? It is a mystery.

I'm not entirely sure if I want to see Epic levels or not.

[Arkhios]

levels from 21 to 30 have already been addressed in the Dungeon Master's Guide. Characters no longer gain levels, but can gain other types of rewards.


OTHER REWARDS
As much as adventurers desire treasure, they often appreciate other forms of reward. This section presents a variety of ways that gods, monarchs, and other beings of power might recognize the characters' accomplishments, including supernatural gifts that give characters new capabilities; titles, lands, and other marks of prestige; and boons that are available only to adventurers who have reached 20th level.

One such option might be a supernatural gift, in the form of Blessing from a god or such. Examples include, but are not limited to:

Blessing of Health. Your Constitution score increases by 2, up to a maximum of 22.
Blessing of Protection. You gain a +1 bonus to AC and saving throws.

...to name but a few. I won't copy them all here, as that might be seen as a copyright infraction. And besides, if you're not a DM, you shouldn't worry about such things anyway. DM will grant the "epic stuff" only if and when he or she sees fit. Not from a player's demand. If you are planning to be a DM, you can find all the details from pages 230 forward, in Dungeon Master's Guide.

[eastmabl]

Someone did it on DMs Guild.

[ZenBear]

I plan on homebrewing some Epic Destinies ala 4E. No ASIs, that's covered in the Epic Boons section noted above, but some fun new features and abilities that describe your ascension toward immortality, godhood, devilry, etc.

[Inevitability]

I plan on homebrewing some Epic Destinies ala 4E. No ASIs, that's covered in the Epic Boons section noted above, but some fun new features and abilities that describe your ascension toward immortality, godhood, devilry, etc.

This. 4e's epic destinies were great.

[obryn]

I think if by "they" you mean WotC the answer will almost certainly be "No."

WotC is largely not in the selling-RPG-books business these days, and even less in the writing-RPG-books business these days. Instead, they are managing the brand, working with contractors, and taking a share of online marketplace sales. I would not expect any kind of generic sourcebook of any kind unless you see a significant ramp-up in their staffing; any future rules will likely be rolled into settings and adventures.

My hunch is that your best bet is to hope an enterprising fan creates something solid and puts it up in the web store.