But what non-western nation has an easy way of coring London and Oxford before WotR ends? From the south, you would need to eat and core a province of Portugal, Castille, France or England, from the Northeast either Denmark or the HRE.
Every Eastern and Ottoman tech nation in the game, or that is everyone who currently has access to the decision.
If your capital is in Europe you can just declare war on somebody in Ireland, vassalize them, and them use that for coring range (I can't recall if you can just vassalize one of the Irish OPMs or if you need to vassalize one, take out an adjacent one, and then core the land of the second). England itself has several viable releasable vassals (e.g. York or Cornwall) that can let you core the place with just a few provinces (e.g. if we make Oxford the important province, you can take Cornwall, Glouchestershire, and Oxford, release Cornwall and then core inland). As long as your capital is in Europe, life is fine here.
Nor is it particularly hard to hold London and later back fill to core it up if they ever nerf the vassal tricks. Starting from the south you can hit up Grenada, Portugal, Brittany, and get coring range to England. From the East, Denmark is normally a pushover unless they ally Poland once you support the Independence of Sweden; even with a Polish alliance you can normally do okay with enough galleys to hold the straights and just take the Danish islands. Moving on from there, you just need to there, if you take the Islands, you might need to alliance chain into East Frisia, but completely doable.
Even taking the hard route via the HRE, is not actually bad if you can ally the emperor, just get into a joint war and then pick off some OPMs with poor allies, preferably when they all killing each other in one of their eternal wars that breaks out whenever the emperor is looking the other way. Sure you have to overcome distance and likely religion penalties, but common rivals, gifts, and nearby conquests (like Venice, East Frisia, Bornholm or Provence can help.
Absolute worst case scenario is something like this, I no-CB Ulster ASAP. I vassalize it. For some reason I'm not based in Europe, so I wait 10 years to annex the sucker. WotR fires before I can annex them. So I declare on England (supporting the rebels), when England is mostly beaten, but the last fort has not fallen (and I take care that I control the sieges, not the rebels), I declare on Scotland & take control of Ayrshire (needs only be momentary). I transfer control of Ayrshire and a path of provinces to London (or Oxford). I make peace with England - taking London via Ulster and grabbing land on the Scottish border. I make peace with the Scots for the English land they want. Now I have long truces with both powers, I annex Ulster, and if Ulster hasn't cored London, I can do so with my new coring range. Pretty much I can pull all this off with a medium rank power or maybe even a minor, as long as I don't have TI to worry about and can build transports anywhere in the Med or Black Seas.
England is isolated territory, it has few natural allies, none of whom are good at supporting fighting on the Isles themselves. It has multiple major rebellions early
and the king is 0 mil leader that I can almost always beat to good mil tech. As an added bonus it likes to fight in France, often has wars with Scotland, has few forts on the Isles (so you can covered just about everything with just one fort falling).
Vienna and Prague are both deep inland with major HRE states to actually take the territory from. Neither have anything like the English rebel troubles nor the English mil tech hole. Likewise, there are strongish states right on the border (Hungary, Poland, Venice, Austria, Bohemia) who will likely pounce on a weak state holding choice real estate. Danzig is easier to take, but Poland has an insane modifier to take Danzig.
Sure some games taking and holding Danzig is easier than taking and holding London, but those are rare. London, Venice, Rome, even something like Amsterdam, Lisbon, or Stockholm is likely too easy to grab in most games. Madrid is likelier easier than Danzig and Paris might be as well (though I doubt it), but so many of the great western cities are far, far too easy to take early in the game.