On the most basic argument, any additional top league in English football featuring the Old Firm rivals Celtic and Rangers would put an end to the long serving tradition of British football. As a kind of "thank you" to inventing the modern game, the four Home Nations are awarded four separate seats on the FIFA and UEFA top tables; England, Scotland, Northern Ireland, and Wales. Okay, we're not quite unique in this, France has a separate international team within its borders, but I won't give away this pub quiz answer today....
For Celtic and Rangers to become permanent, full members of the otherwise English Premier League, the whole future set up of the national and international game would change forever. UEFA and FIFA have made it quite clear that a separate English international football team would not exist were the Old Firm to become members of any national football division. Remember the fuss regarding Cardiff winning the FA Cup not being able to take part in European cup competitions? Think about that writ large.
If the idea of a joint Anglo-Scottish football team doesn't jump out at you (oh imagine the pubs before kick-off...), what about the future of the lower leagues? The amount of money trickling down to even League 1 and League 2 levels is not torrenting down in great waves; an increasing number of Conference and non-league sides are up against the financial wall including Hyde, Farsley Celtic, and Chester. The possibility of having a "walled garden" outside of which survive a withering clutch of barely solvent league teams is nothing short of offensive.
"Mighty" Anderlecht are about discussing the "Atlantic League" theory in case a British "Premier League 2" falls flat. If the notion of pan-European league fills you with a logistical shiver down the spine, you may not be the only ones. But the future of British football, which is far more than sepia-tinged nostalgia for half-time pies and giant killing, relies on the four Home Nations having leagues of their own. Cross-border leagues do not exist in any other country in the world; for clear and unique reasons, the United Kingdom does not suit the notion of a grouped league football format.
Healthy and economically strong our football teams are not (Spurs aside, and there are rather dodgy non-politically correct suggestions for why...). Bringing English and Scottish leagues together in any form would merely produce an incredibly exclusive clutch of world-famous franchises kept away from the motley crews (and indeed, Crewe) below. As a fan of football, and of the lower league game specifically, the prospect does not thrill me with joy at all.