Need to be careful here. The Rhine was opened to free navigation for nations bordering it as a result of the Mainz Convention of 1832, with a similar convention for the Danube signed at Paris in 1856 after the Crimean War.
Nations like Switzerland, or Austria, Hungary and Czech post WWI were not "Cut off from the sea" in the sense that they could ship their goods down and import goods up these main commercial arteries without paying any tariffs from countries further downstream.
And Switzerland was already well industrialized by the 1880s, so yes well within the Victoria timeframe Switzerland was an industrial power, taking advantage of its neutral status and its free access to the Rhine to develop its industrial potential.
Now, during wartime access to the sea is a vital question, and treaties such as the ones regulating the Danube and Rhine were not in effect if nations along their routes came into conflict, but during times of peace I don't think there should be any maluses regarding access to the world market for landlocked nations. Systems for ensuring access in peacetime were in place.
The importance of rivers is a subject that I hope sees greater attention paid in V2. In this time, the Danube was a greater means of internal, rather than international commerce due to tariffs at the Iron Gates and the CED tariffs at the mouth, nevermind the silting that limited ocean access to empty vessels. I will be pleasantly surprised if the game engine can handle these matters.