I am in full support of this. Beatmap packs are too difficult to find and you can never know what is in the packs before you download them. It would be incredibly useful to have an ingame method of knowing what is in the pack before you download it.
Here is how I imagine it working.
There is a button that switches to beatmap pack mode. You can view various packs, or filter just the achievement packs. You can also type in a pack number and it will tell you all the songs that are in that pack. It would be a very good system for downloading mass beatmaps.