The elephants in the room that everyone ignores when comparing the UK TV market to the US market are the BBC and Channel 4.
The US model doesn't have two well-funded, popular, public service broadcasting TV organisations - commanding a 1/3rd of the viewing audience before any of the other networks make a start. Plus BBC One is the most popular channel in the UK.
That does make a significant change to the ecosystem - plus the US has a mix of O&O and Affiliates, plus network production, and syndication - which doesn't really map to any previous UK model does it? (The ITV model never really had separate network production - all non-indie productions were made by individual franchises, which would equate to large US local stations? ITV didn't have a separate 'network' production operation until it became ITV plc)
The US has PBS though, which is different again. Additionally, Japan, which also has regional networks has NHK; the state broadcaster more akin to the BBC. Each region has two NHK stations as well as the regional commercial ones. The NHK stations are organised on the same regions, similar to how there is a regional BBC service in each ITV region (even if they don't always align).
If the London split was removed (along with no archaic breakfast franchise) and ownership was relaxed so that one company could own three or four stations, then it's not hard to imagine a London-based network developing as a result, with O&Os in London, West Midlands, North West & Yorkshire, as I said in my previous post. One aspect of the US system that's always fascinated me is how if a local station forgoes a network offering, the network has the right to offer it to another station in the same area; even if it's affiliated to a rival network. Kind of reminds me of when Carlton were threatening to axe Emmerdale. Syndication is also interesting, with local stations purchasing blocks of programming; sometimes repeats of old shows, sometimes imports, often quiz shows and the like. It's quite dynamic in some ways.
But this is all just a thought exercise; albeit an interesting one.