The difficulty bomb currently is being discussed in two opposing proposals. Rather than having to follow two comment threads, this thread should merge the debate.
EIP-649 established a delay in the difficulty bomb and reduced the block reward as part of the Byzantium fork. The bomb was originally included in the metropolis HF with the intent to provide leverage in the transition to PoS as there was not a clear governance process in place to enforce the project roadmap and was to be used to make mining increasingly unprofitable. In the interim 2 years the community has grown considerably and the transition to PoS is now a universally understood matter of ‘when’ not ‘if’.
As it is currently implemented, under EIP-649, the difficulty bomb will soon begin to become a determent to network difficulty and block time again. As such, the Constantinople fork is the logical junction to implement a change in the bomb. Two opposed EIPs have been suggested, EIP-1234 and EIP-1227.
Abstract: Starting with CNSTNTNPL_FORK_BLKNUM the client will calculate the difficulty based on a fake block number suggesting the client that the difficulty bomb is adjusting around 6 million blocks later than previously specified with the Homestead fork. Furthermore, block rewards will be adjusted to a base of 2 ETH, uncle and nephew rewards will be adjusted accordingly.
Abstract: Starting with FORK_BLKNUM the client will calculate the difficulty without the additional exponential component. Furthermore, block rewards will be adjusted to a base of 5 ETH, uncle and nephew rewards will be adjusted accordingly.