Since no way to convert power from one form to another is 100% effective you would get a net loss of power if you used an electric boiler to generate electricity with a steam engine anyway. This is probably the reason it is made to not connect to steam engines. Think about it, you would generate electricity with the steam engine from steam created with electricity. If you could get more electricity out of that loop than you put in it wouldn't make much sense.
There are things in the space exploration mod that needs steam for manufacturing I think. In that context an electric boiler makes more sense, especially if said manufacturing is in space.