Summary

TLDR = BU fork will only be added to exchnages with proper replay protection and it will be an altcoin called BTU / XBT

https://www.scribd.com/document/342194766/Hardfork-Statement-3-17-11-00am
https://fs.bitcoinmagazine.com/assets/exchange_handling_of_contentious_hard_fork_event.pdf

20 Exchanges in the document that say the original chain with remain bitcoin / btc regardless of outcome :

Bitfinex, Bitstamp, BTCC, Bitso, Bitsquare, Bitonic, Bitbank, Coinfloor, Coincheck, itBit, QuadrigaCX, Bitt, Bittrex, Kraken, Ripio, ShapeShift, The Rock Trading and Zaif

2 signers agree with document but place an exception that they reserve the right to rename BTU as BTC if the supermajpority switches :

ShapeShift  - If BTU sees 95% it wins the name BTC, otherwise the original chain remains BTC -
https://twitter.com/ErikVoorhees/status/842830189474136064

Kraken - At their discretion - https://www.reddit.com/r/Bitcoin/comments/5zz6cu/important_the_exchange_announcement_is_indicating/df2fnyz/

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2 more exchange joined this list :

21) Bitmex  

https://twitter.com/BitMEXdotcom/status/842796617120059393

https://blog.bitmex.com/a-statement-on-the-possible-bitcoin-unlimited-hard-fork/

22) poloniex
  
https://poloniex.com/press-releases/2017.03.17-Hard-Fork/

https://twitter.com/Poloniex/status/842789390518812673