Belwas was supposed to come along with Arstan Whitebeard but now that story line has ended with the death of Selmy then it does leave the door open for Belwas to be a part of the show. He's missed his chance to fight into Yunkai but I can imagine him being there to eat the poisoned locusts that are meant for Dany at the great pit fight. Tyrion does owe the big fella for releasing him from his chains and a Lannister always pays his debts so could imagine Tyrion wanting him along as a bit of personal protection.
Only briefly scanned through all 46 pages of this thread (you guys are frantic posters) and I've not seen any mention of Tyrions chain breaker. Personally I'm thinking it could be Strong Belwas making an appearance. Was he credited? It would make sense if it was Belwas, he was a pit fighter and someone I've missed from the books.