I always thought "Ho" was just a case of the special kid in the class trying to be different. It's an unnatural form of expression. Across English, French, German, Spanish, Japanese, and Hebrew, you have words like "Ah!", "Aa!", "Oh!", "Ay!", and "Oi!" These exclamations all begin with a vowel and, arguably, are entirely vowel (the "Aa" and "Ah" sound are the same; "Oh" is just "O"; "Ay" is a dipthong "Aa-ee", as is "Oi" or "Oy").
Vowels are produced with open, maximum airflow. Exclamations in this form are derived from surprise, dismay, anger, and other forms of strong emotion. Their biological basis is a warning cry, which means they begin with a form capable of providing the most power--a vowel.
"Ho" begins with a quiet, non-voiced, constrictive sound. For the expression it represents, it is completely unnatural. It's the most-likely candidate in the entire language for replacement by natural linguistic evolution rather than cross-language intermixing, and probably would have been replaced long ago if the number of native Esperanto speakers (~1,000) weren't hilariously outnumbered by academics (~2,000,000) trying to hold this ridiculous particle rigid in its pure, historic form.
Inb4 everyone starts arguing the H is silent.
What about laughing? It seems to me the H-sound is used rather often to express surprise, although it is generally on the minor side; "huh?," "hunh??," "ha!" and "hey!." for example.
Actually in Japanese there is a exclamation that begins with H. ほうほうほう(、これはこれは)。It's not that common in modern language, but still exist.
Zamenhof was a native Yiddish speaker. I love these (few) Yiddish parts of Esperanto :) The only other one I'm aware of being "nu". Even lojban uses oi to express complaint.
Ha, yay! I typed "oy vey" totally expecting to mark "my answer should be accepted" and was pleasantly surprised
One can't help but wonder if Santa Clause is an Esperantist traveling across the sky saying "Oh... Oh... Oh..."
I wonder if "Oh oh!" would be accepted. (Not sure if that spelling conveys just how it's pronounced though).