Bitcoin Core is the original bitcoin node software and its developers want to due away with the 80 byte max size limit for OP_Return data in a bitcoin block. This would allow for OP_Return data up to the size of the bitcoin block weight which is 4MB (four megabytes).
What is OP_Return? Its an Opcode which means it’s a function or command in the Bitcoin software and this particular one is used to add arbitrary data to a bitcoin transaction (or an output of the transaction, you can have more than one output in a transaction). It renders the output as unspendable so it’s not sent to a bitcoin address but the data is recorded to the Bitcoin blockchain. You don’t have to include bitcoin in the output but if you do it will be lost forever (burned).
Originally there wasn’t a size limit for Op_Return but it was later set at 40 bytes and then again later on at 80 bytes.
Bitcoin Knots is a bitcoin node software implementation by Bitcoin Core developer Luke Dashjr. Knots will not support removal of the 80 byte size limit for OP_Return data.
Either way (Core or Knots) the official block size will remain at 1MB and total block weight will remain at 4MB. The sum of block size and block weight cannot exceed 4MB.
By increasing Op_Return size to 4MB it will be possible that just one transaction (or just one output in a transaction) could fill an entire Bitcoin block.
Is this good for bitcoin miners? Maybe.
Is this good for people sending bitcoins? Maybe not.
Keep an eye on this topic at the BitcoinTalk forum: Bitcoin Core or Bitcoin Knots, the OP_RETURN debate