“Geth, Parity, aleth, ethereumj, mana, nethermind - completed implementation of all EIPs”
“we should probably pick a block number today for testnet fork”
“Let’s go with Ropsten block 4.2M, that puts us at this time in 11 days, on Oct. 9”
Certain client development stakeholders wanted to activate forking changes / Constantinople in order to identify possible consensus bugs and reduce risks for when these changes are activated in clients for mainnet. This group includes the geth team.
On the other hand, dapp stakeholders who depend on Ropsten stability did not the burden of dealing with a fork, and wanted a stable, enduring testnet for their users/testers. In this case it was the Raiden team.
The key discussion between these groups happened here: https://gitter.im/ethereum/AllCoreDevs?at=5bb5c0b0ef4afc4f281795f2