Moscow and London should both be difficult to take, more so than, say, Austria or Berlin. In London's case, I'd do it by isolating the UK further by making the battles around it start with 3 neutrals (maybe not so much St. Vincent since that's surrounded by neutral starts anyway). That would more accurately reflect British naval domination and just how hard it was to attack Britain by sea; it would also reflect just how tricky it was for Britain to invade the mainland.
As for Moscow, you might give it a little auto-deploy, and consider splitting the Kiev territory into two. Those would reflect the tremendous Russian population and the favorite Russian strategy of 'retreat further into Russia until they all die of cold'.
While you're at it you might as well simulate Napoleon's logistical superiority by letting Paris one-way assault certain territories like specific battles, French-allied capitals, or just external adjacent territories.
We increased Moscow to +4. Russia now has 12 territories, 1 more than the fully expanded French Empire. It also has the 4 winter territories. It is therefore already difficult for a player to consolidate the Russian empire (as is on the Europe 1914, map, where Russia has only 10 provinces, no winter effects and only 3 neutrals on Moscow). We did in fact have 13 terrritories for Russia, but we were worried that leaving it at that number might make it practically impossible for a player to conquer it and obtain a bonus for it. This being said, I'm all for leaving the option open to add one more territory, depending on feedback on balance and playability.
I had the same thoughts on Napoleon as you did and wanted to use rivers for this purpose (Rhine, Rhone, Garonne, Moselle) but the map would have become way to charged with details and, possibly, confusing. The way we have tried to simulate the Emperor's logistical superiority is by allowing France to get an initial bonus for its pre-Consulate boundaries, and having 5 battles and 4 empire territories within easy grasp, for additional bonuses of +8 (3 for 5 battles, 2 for Empire territories, 1 for Kingdom of Italy).
I know exactly what you mean to propose with Russia and France for historical purposes, but I fear the aggregate effect would be to make it evern more difficult still to unite Russia and much easier to build the Empire and defend it - all of which has the potential to unbalance the game.
In short, we did indeed increase Moscow starting neutrals to +4, we may add one more Russian province, and I would be willing to consider increasing all Naval Battles to +3 neutrals to shore up the UK's defences, and increasing France's empire bonuses from +1 for every two territories, to +1 for the first two, then +1 for each additional one (thus making two extra bonuses available to it for conquering the full Empire.
Let's see now what Kab, Andrew and Nobodies think....
Again, thank you very much for your suggestions.