I understand that this isn't as sweet as what you are asking for, but I wanted to inform you that it is possible.
Paying members has access to something called Custom filter. Combining those with for example map compare, one can find caches with specific attributes. It is a bit clumsy for this and you have to know which attributes you need, but it is a workaround.
But I like the feature suggestion, haven't heard i before, and I am surprised I did not think about it myself. It's likely to be implemented at some point.