Just checked; my cache is 3.9M (last time cache emptied on 23rd).
The amount of cache actually depends on your site, on your autoptimize settings (another user noticed that when setting "only look for js in head" and the same for CSS), the amount of cached files dropped significantly) and on whether of not you use a plugin to do HTML caching (e.g. wp super cache or hypercache, which you really should have).
But I do understand that under certain circumstances better cache management would be ... nice. It's on my wishlist, but can't make any promises as to when it'll be implemented. But I do welcome code-contributions ;-)