This sounds similar to the idea discussed in a recent thread - Restricting connections between custom nodes - and I think the conclusion, and certainly my thought, is that restriction connection types is not really a good idea for several reasons. For example, new nodes might be unable to connect to yours even though it would be valid, or someone might think of a clever use for your node but be unable to link to it.
Can you maybe describe the sort of use-cases where restricting connections would make sense, and not limit future uses of a node?
