When we do this we can probably rename the transient back to perflab_plugins_info

Yes, by then any existing transients with the old key should have expired as well.

While the idea behind this enhancement makes sense to me, we need to be cautious about this: The reason it's implemented the way it is now is to not cause endless re-attempts of the request when plugin data is not available, which can temporarily happen for one reason or another. In other words, failed lookups still need to be cached.

We will need to implement this in a way that differentiates between:

• Was plugin data not found by the request?
• Is plugin data not present in the cache because the plugin was newly added to the list in Performance Lab?

I would suggest we do something like cache a value like false for every plugin that we requested data for at the time of the request. This way we can differentiate between ! isset( $plugins[ $slug ] ) (new plugin, so ignore the cache and make the request) vs ! $plugins[ $slug ] (plugin data was already requested but not found).