The Bitcoin network is incapable of identifying miners at the consensus layer. To put it very simply, all that the network sees when a new block is added to the blockchain are the block's contents (i.e., the transactions in the block) and its metadata (i.e., the block's hash, the block's merkle root, the block's size and weight, etc.). There is no indication whatsoever at the consensus layer of which entity mined the block.
The identity of a particular block's miner as shown by block explorers — e.g.,
Blockchain and
Blockchair — are simply guesses by the block explorers themselves, based on various block attributes such as the block's coinbase text and the output(s) in the block's coinbase transaction. There is no indication whatsoever in the block itself that mining pool X or miner Y was the one that mined the block.
Even hashpower estimates by block explorers are mere guesses by the block explorers themselves, based on algorithms that take into account, among other things, the time interval between blocks.
There is therefore no way for the Bitcoin network to distinguish between the top 50% or the bottom 50% of mining power at any given time, making this proposal unfeasible.
Even if there is a feasible method of distinguishing between the top 50% and the bottom 50% of mining power — e.g., through the use of
oracles — such a method would most likely require a hard fork. Given how messy segwit's soft fork was (it wasn't even a hard fork), I highly doubt that such a proposal would even get past the proposal stage. And that's not even including the fact that the hard fork would need to add a sidechain mechanism for the altcoin portion of this proposal.
Even if, by some fluke, the Bitcoin community — developers, miners, and users — agreed to the hard fork, such a change would then open another can of worms. Now that the Bitcoin network would be able to identify a particular block's miner(s) at the consensus layer, and now that the Bitcoin community has been emboldened by a successful hard fork that supposedly mitigated the centralization of mining power, what's there to stop Bitcoin from undergoing new forks (soft or hard) that prevent certain miners from mining new blocks once they are deemed to have too much mining power? While this may seem like a good thing on its surface — mining pools would be further disincentivized from amassing more than 50% of Bitcoin's mining power — this essentially introduces an element of censorship into the network at the consensus layer and sets a precedent for further censorship. Mining pools would, of course, evade such censorship by splitting up their mining power to appear to the network as multiple discrete entities — i.e., a Sybil attack.
Not nodes. This altcoin reward goes to Bitcoin block producers only.
A Bitcoin full node — e.g., Bitcoin Core — is a block producer's only interface to the Bitcoin network. Without a full node, a block producer would not be able to submit any new blocks to the Bitcoin network, in the same way that without a web browser, an Internet user would not be able to access the web.
