The hostcache would be very easy to create. It should be made compatible with the GWebCache so clients that existing clients ( such as Gnucleus ) can use it.

The tracker could be a good idea if implemented correctly. I assume you would want it to function like a QueryHit cache. If it is to be used for client applications it could be of benefit. If you intend to allow web users to access it ( ie Browsers ), it could be bad for the network since the users downloading will not be uploading. This would be bad because clients that are actively participating in the network will have a harder time downloading. Also, I believe at least a couple of clients may be blocking web browsers.

In any case, if you would like some help creating these I would be willing to help.