Sorry to be late to respond, got problems with my PC lately.
users incentivize miners to put this or that transaction into their block by actually paying a fee.
Correct. But it does not mean a miner HAS to accept your transaction, even if you paid the fee. The fee does not give you the right to force a miner to mine it.
Protocol change must be universally agreed upon by the whole network to be legit. Bitcoin isnt about playing politicians here, with roundtables and bribes or what not. Soft forks are a devious way to contort the rules without consensus. If you were so confident about the relevance of the VC market pull "upgrades" you are so eager to shove down the protocol's throat, then you should propose a hard fork it and see how your altcoin goes.
You must distinguish between protocol rules, consensus rules impacting nodes and consensus rules impacting miners.
Protocol rules is made by the node's developers. (xthin, cmpctblock, getutxo, bloom filters or whatever)
Consensus rules impacting nodes need universal agreement, as if it does not, a split of currency can happens.
Consensus rules impacting miners does not need agreement, as the miners were ALWAYS in possession of which transaction they decide to mine in the first place.
If you think a SF is wrong whatever the reason, you should find a way to enforce it in a decentralized manner, and this mean that you must find a way to make it impossible for miners to see anything more than fees in the transaction.
Interestingly, you can implement that in a SF.
