While the split economy cabin was tried before, and did not work, that was long before the advent of the LCCs,and passengers getting used to the concept of paying for all the extras!
It works these days, for example all SAS European flights have Economy plus, and economy, a simple seat placard divides the cabin,
Economy plus provides all the usual economy frills, economy you get one free checked bag, free tea and coffee, but pay for everything else.