Technically we could invest even more time in making megatopics more efficient and possibly move to a system where we cache frequent posters poisoning the cache every single time you modify the topic (for example by posting to it)… but we are simply not motivated to make such changes at the moment.
The number of megatopics in the wild is minuscule, investing large amount of time optimising this means we have less time working on features which are much more commonly needed.