But of course that district has been constructed to give 1 party a distinct advantage. It’s one of the reasons congressional approval is in the single digits on a general poll but 95% of them are going to be re-elected in November. If there aren’t parties constructing districts that problem goes away, you can still have districts without gerrymandering, and the districts become actually useful because the people in them are no longer pre-selected to keep one party in power.
Guys run for primaries now nationally without having to be really really rich. That’s what campaign donations are for. The only real difference in my system is that primaries reduce the field (probably to 5 for president, fewer for lower offices) instead of creating party nominees.
Campaign ads wouldn’t change at all. Primaries would be wide open like they are now, general elections a reduced field. Except of course you no longer have deep pocketed parties buying ads, because their alliances are now informal they’d have to donate to the campaign just like everybody else.
If you had 600 politicians doing full nationwide advertising to get votes to represent the biggest district on Earth, you wouldn’t have time left for other broadcast communication. It’d eat all the bandwith!