To my understanding, "biáng" is not a sound that exists in Mandarin, though there's some argument on the hypothetical phonological possibility of such here. One might assume therefore that it is a character either unique to or else created within Shaanxi dialect (given the alleged origins of the word). If such a character is read by a speaker of another dialect, how would it be pronounced? How might, say, a Cantonese-speaker or Hokkien-speaker read it?
I don't think this is the answer you want but it's the answer you're getting, at least from me.
明末洪帮图符研究 on the Wikipedia page for Biángbiáng面 notes:
王纯五. 洪门·青帮·袍哥——中国旧时民间黑社会习俗. 四川: 四川人民出版社. 1993: 71. ISBN 7-220-02058-9.
The biáng character is used for the pronunciation zuí in Sichuanese and Chongqingese.
The characters, though, have slight variations:
Here's the Chongqing variation
and the Sichuanese variation:
According to the materials they mean the same as 贼 or thief.
Sichuanese/Chongqingese words like:
Could, in theory, be written with biáng instead of 贼.
Funnily enough, though,《广安方言与民俗词典》from Sichuan has also recorded an entry for:
which they have defined as:
The rhyme matches the footnote on Wikipedia for:
So, in Sichuan/Chongqing, is it zuí or biáng?
I guess it depends on the context.
Lastly, according to 辞书收录 on the Wikipedia page for Biángbiáng面:
It would go to show that the majority of dialects would follow the rising tone of [piaŋ24] because after all it is a 陕西 thing.
This character is exclusive to the northwestern mandarin, and read in other dialects simply mimicking the pronunciation in the original dialect. It is just treated like loan words in many languages borrowed from English words, e.g. Computer in German.
Exclusive characters are not typical to the northwest, and in fact every dialect has its exclusive words. The character 覅 (fiào) is the only character with its pinyin beginning with fi- in 《新华字典》 and 《现代汉语词典》, and it is an exclusive character to Wu dialects, pronounced as [viau13] in Shanghainese. Due to its frequent appearance the authorities of Chinese dictionaries choose to include it, to some extent as a 'loan word' from Wu dialect to the modern standard mandarin, which is only a variant of generalized Chinese.
I think we don't need to consider its pronunciation in other dialects, because this character Biáng doesn't even exist in the formal Chinese, it is brand new to people from other regions.
入乡随俗 Do in Rome as Rome does
Biángbiáng miàn is a Shaanxi speciality, it took its name from the sound made in the production, see here for details, in my view it doesn't matter where you come from, you should be interested in learning their culture and history