The 50MB size limit is quite expansive for a texture pack, but with the new resource pack system, a pack can have other purposes. The pack I use on my server happens to be a sound pack.

Unfortunately, OGG files apparently take up a lot of space. So even excluding the sound-effects, 50MB is not even enough for all of the songs in the game to be changed. At normal compression, you get around 62MB, and high compression brings it down to around 55, but takes longer to load. In this case, each OGG is at 96 kbps, any lower and it would just sound awful. Therefore, I think the limit should be increased to 70 or 80MB.