Code:
getmemorypool [data]
If [data] is not specified, returns data needed to construct a block to work on:
"version" : block version
"previousblockhash" : hash of current highest block
"transactions" : contents of non-coinbase transactions that should be included in the next block
"coinbasevalue" : maximum allowable input to coinbase transaction, including the generation award and transaction fees
"coinbaseflags" : data that should be included in coinbase so support for new features can be judged
"time" : timestamp appropriate for next block
"mintime" : minimum timestamp appropriate for next block
"curtime" : current timestamp
"bits" : compressed target of next block
If [data] is specified, tries to solve the block and returns true if it was successful.
If [data] is not specified, returns data needed to construct a block to work on:
"version" : block version
"previousblockhash" : hash of current highest block
"transactions" : contents of non-coinbase transactions that should be included in the next block
"coinbasevalue" : maximum allowable input to coinbase transaction, including the generation award and transaction fees
"coinbaseflags" : data that should be included in coinbase so support for new features can be judged
"time" : timestamp appropriate for next block
"mintime" : minimum timestamp appropriate for next block
"curtime" : current timestamp
"bits" : compressed target of next block
If [data] is specified, tries to solve the block and returns true if it was successful.
And a meta-question: are there any other implementations that will be supporting external mining via JSON-RPC soon? There's no reason to go through the whole BIP process to make a change or improvement to one implementation.