If your node sends out a list of mempools from all the nodes connected to you, while all the other nodes are doing the same, surely that's fair amount of information to broadcast and much of it would be repeated unnecessarily.
If node send MEMpool stats (size, number of transactions), the listener can use the 8-25 connexions to build an average size & number of transactions.
With this, it can recalculate the fees if MEMpool is satured (Blockchain.info store 2Gb ... but malority of nodes store 300Mb, right ?).
An SPV wallet can use this average info with her 4-6 connexions.
Okay, so each node would only send its own mempool, not a combined list of the mempools from all the nodes connected to it? That would be more efficient and would probably make refreshing the details and having to rebroadcast them again trivial in terms of resource consumption. However, it seems
there are still some limitations, even if sourcing from multiple mempools:
Fee Estimation based on current mempool
A naive fee estimation algorithm would look at your mempool and set your transaction fee at a level that puts it in the highest-paying 2MB of transactions. You might expect that strategy to get your transaction confirmed in the next block. Unfortunately, it’s not quite as simple as that for a number of reasons:
Very recent transactions may not make it into the next block. Miners are already working on the next block when you submit your transaction. Depending on how they refresh the block as they work on it, they may not include your transaction.
Whatever time you send your transaction into the mempool, the expected time you’ll have to wait for the next block is 10 minutes. This is a fundamental (and often misunderstood) property of the Poisson distribution that block discovery follows. If you place your transaction into the mempool 8 minutes after the previous block, the expected time you’ll need to wait isn’t 2 minutes — it’s another 10 minutes. Therefore you’re not just competing against what’s in the mempool now, you’re competing against what’s going to appear in the mempool over the next (probably) 10 minutes.
Looking at a snapshot of the mempool doesn’t take into account the fact that there will be lucky runs of blocks and slow runs of blocks in the future. It might give you some information about how much fee you need for your transaction to be included in the next block or two, but can’t tell you anything about how much fee you need if you want your transaction included in the next 100 or 200 blocks.
There's always going to be some guesswork involved, as the goalposts are constantly moving.
