1st suggestion:
Have access to ALL (including private ones...Somehow, maybe the replay page recognizes the logged-in account at play.pokemonshowdown.com? Login your account in the replays page? Access to private replays here in the forum? I don't know, just one way to view) your saved replays(At this moment have a limit of 502 replays for each nickname);
2nd suggestion:
When downloading a private replay, show the link like;
http://replay.pokemonshowdown.com/ (If the replay is private and only you have the download.. you can't pass it to a friend unless if you have the link of the replay);
3rd suggestion:
http://bulbapedia.bulbagarden.net/wiki/Shadow_move
Put those moves (and maybe shadow pokémons too) in the Pokémon Showdown. Maybe only in generation 3 can use this (can use in the custom game also, that neither bersek gene that has in generation 2 but can be used in custom game). You could also make a kind of OM, tier, etc.
For now, it's this.