The current replay archive is something like 8gb i'm told. So clearly there will come a time when we start to remove old replays - probably just the dismissed ones. However with the cost of storage these days its probably cheaper to buy a new hard disk than to spend time coding extra functionality into old features.
The fact we delete replays at all isnt what i'd like to have, i'd like to archive every race and offer full statistical analysis of it, but that becomes a huge amount of data very quickly.
However it was always the intention to keep replays of lap records [since the concept was raised a little while ago], the fact the system wasnt doing that was a mistake on my part. I spotted it recently and got some updated code from Sam to fix it and thats been live a little while now.