I've just been reading a review of a new book about the 1879 FA Cup Quarter-Final between Darwen and Old Etonians.
The tie went to a second replay but all the matches were played in London as the Old Etonians refused to travel to Lancashire and the FA declined to intervene (no change there). Like other Northern teams, Darwen's players were working men and as amateurs had to find the money to travel to away matches from their meagre wages, unlike the sides made up of ex-public school boys who dominated the FA Cup in the first decade of the competition.
By the 1880's, Northern working-class teams had begun to compensate their players for expenses and lost wages and some also surreptiously employed professionals, many of them from Scotland where the "passing game" had been invented in the early 1870's. This led to the FA threatening to throw the Northern teams out of what was still officially an amateur game (there was also a proposal to ban Scottish players from English football in order to stem the tide of professionalism). Thirty-seven Northern teams responded by meeting in Manchester in 1884 and forming the openly professional British Football Association.
All this is of course an almost exact parallel with what happened in rugby football in the 1890's: the threat by the amateur Rugby Football Union to expel Northern working-class teams for paying players and the meeting in Huddersfield in 1895 that led to the separate game of rugby league. The FA headed off a permanent split in football by legalising professionalism in 1885 and in 1888 the Northern clubs met in Manchester to form the Football League as a league competition alongside the FA Cup. But what if the FA hadn't sanctioned professional football? Would amateur football in the South and professional football in the North have continued to be played under the same rules or would they have grown apart like rugby league and union? Would professional clubs like Arsenal and West Ham still have emerged in London and the South to challenge the amateur FA? Would they have eventually linked up with the professional Football League clubs in Lancashire and the Midlands as they did in the early twentieth century?
I think football would be broadly similar if the split between amateurs and professionals had continued and the Football League would still have expanded from its Lancashire birthplace to the Midlands and then the South in a way that rugby league didn't (apart from to Australia, and you can't get much more Southern than that).