-Sweeden would have probably been overrun by Russia. As mentioned before their military wasn't up to date and numbers alone would favor Russia. Between this and the Finnish rebellions this could tie down a good number of troops from the main front against Germany and Austria-Hungary. Why would Russia do this though?
See the mentioned "von Essen" threads, I doubt Sweden would be overrun, it almost impossible for Sweden to be overrun through the north, and the German High Sea coulsd roam the Baltic freely sabotage any naval invasion of Sweden (Sweden would likely occupy the Ålands rather fast, but have little succes in contignental Finland), but Sweden would likely grow more and more dangerous through the war when it modernise.
-There's a reason the British didn't try any amphibious moves against Germany. It'd be a logistical nightmare. Denmark might be initially easier, but the terrain is a natural bottleneck so it wouldn't take many German reinforcements to bog the front down. Only real advantage of this I see is it'd give the Royal Navy access to the Baltic.
With Sweden in the war, access to the Baltic is a very good reason, it would cut Sweden of from German support and open Russia up. So with Sweden in the war there's enough reason to do such a stupid thing.
-Invade Switzerland to hit south Germany? Okay... let's lay off on the wine. Instead of fighting to defend the main thrust of the German attack, you're going to divert several thousand troops in an attempt to cross some of the most rugged terrain the world has to offer, against a country that hasn't been successfully invaded in some 500 years. The Swiss wouldn't even have to use guns, they could just roll rocks down on the attackers and probably beat them back.
While I have a hard time to find a good reason to invade it, Switzerland defensiblity is quite overrated, must of the north where the majority live is no worse to invade than South Germany, if not a lot easier, if the allies decide to invade, the Italians would fast occupy Ticino (through no more), while much of west Switzerland would fall to France, the only thing save the rest of the north would German reinforcement, my guess is Switzerland west of the lake Neuchal would end up in French hands.
So in conclusion, if the three major powers of the Entente all decided to do something monumentially stupid, yes there's a good chance the Central Powers(not the Axis, wrong war), would have won.
I wrote CPs not Axis. But yes these military disasters give the CPs a better chance.