There is one chest located near three of the shrines on the Great Plateau. The chests all have 'EX' on them, so it's easy to tell if they are the DLC ones.
The first chest is located right next to the Oman Au (Magnesis) shrine, on the left facing the entrance. Contains 1 Ruby.
The second chest is located on a wall near Ja Baij (Remote Bomb) shrine. Exit the shrine and look up and to the left. Contains the Nintendo Switch Shirt.
The third chest is located near Keh Namut (Cyronis) shrine. Fast Travel to the shrine, turn around, and go behind the shrine. It should be on a wall to the right. Contains 5 bomb arrows.
Shrines (and their corresponding monks) can be linked to Zelda staff members.
According to this wiki page on gamepedia:
Oman Au is an anagram of Aonuma.
Eiji Aonuma is the lead producer for The Legend of Zelda series.
The Japanese name of the shrine is マ・オーヌの祠 (Ma Ōnu no Hokora), meaning Ma Ōnu Shrine
The Italian name of the shrine is Sacrario di Mau Ona, meaning Mau Ona Shrine.
The French name of the shrine is Sactuaire de Ma'Ohnu, meaning Ma Ohnu Shrine.
These are all anagrams of different translations / romanizations of the name Aonuma.
Quoting from this video of DidYouKnowGaming:
Aonuma is not the only developer that was referenced in this way:
Other monks and shrines are also named after zelda staff:
Zalta Wa Shrine -> Satoru Takizawa ( Art Director )
Sasa Kai Shrine
-> Hiroshi Sakasai ( Designer )
Katosa Aug Shrine -> Katsuhisa Sato ( Physics Programmer )
Naming each shrine and monk after a member of the staff was actually
suggested by Satoru Takizawa himself.
Based on these examples, not all shrine names are direct anagrams of staff member names, which might make correlating more names to staff members a bit more difficult.
It is still unclear to me whether such a link does indeed exist for every shrine/monk, or that this was only suggested but never fully realized.
Following the sources in the description of the DidYouKnowGaming video,
I came back to gamepedia, which has a page with namesakes for many more monks.
Interesting to note is that on the same day I originally posted this answer, a user named TriforceTony added a lot more names to this list!
Best Answer
This article gives directions on where you can find what appears to be the ruins of Lon Lon Ranch.
Here's a video that shows the location, as well.