Very informative, so,

If multiple node/mining types can support Bitcoin how do these same types then also support different currencies, e.g. Bitcoin Cash and Bitcoin Unlimited, along with Bitcoin?

If Bitcoin isn't a democracy then is it exposed if one entity controls >50% of node/mining CPU power + the developers of the leading node/software type e.g. Bitcoin Core. Maybe the entity could implement whatever protocol changes/consensus rules it wants?

It seems after all coins are mined then transaction fees will be the only motivational force for mining.