My personal opinions (sorry if this turns into a wall fo text or a rant).
At the moment in PWO players are spoonfed pretty much everything they could ever need to wonder about in the game - in terms of pokemon they can find out all the ever need to know by using a few commands, they will know exactly what pokemon are found on what map and how difficult it will be to find them. You might think this is good as a player but for the game it is bad, it kills player discussion - why do you need to ask when you can just have the game tell you itself, it turns people away from our commnity as they do not need to use the forums or the wiki or the playerdex as the game will tell you everything itself, they never even have to ask in chat about a pokemon they might want. It kills discovery, it kills hope, when everything is known there are no surprises there are no discoveries and everything is just left bland - it gets stale. That is the big problem I have with it (amongst other 'features' of the game currently) they all add up to cause a stale experience over time.
Looking into the player perspective, how many of you can say that you have based pokemon values from there 'rarity' tags? What is a Rare worth? A Very Rare? A Horribly Rare? Now add shinies to this, how many pokemon are valued by people based on being a S Rare or a S Very Rare? The market is stifled by these self imposed caps and while it may be a bit simplistic here and other factors like IVs and battle strength are used it cannot be argued that these tags add a pointless supply limit to certain pokemon because of these rates, rates given to players by the /list command. I can't say for certain but I feel that the rarity changes coming and the removal of the /list command would give a more dynamic market for players.
As a staff member I see the same thing every event in PWO - people will find out about the spawns the instant they are able to, they will buzz for a short time about whatever pokemon can be found and then everything goes into the same week or 2 week long grind for the HRs. Again I feel this is another stale aspect of the game, but if there was no way fo finding out the spawns beforehand what would it be like to walk into a new area not knowing what you could find. Wondering whether this pokemon could be the events HR, being the first person to find that rare pokemon would become something special, there is no predetermined pattern set for the event because you don't know what is going to happen, you don't even know if maybe, just maybe, there might still be that 1 rare pokemon that no one has found yet. Do you see the potential even a small change like this could bring? There would be people actively discussing what they think are the rare pokemon and which are the more common, people working out together things that were previously just given. A community effort brings a lot more to a game than an Umbreon spawn.
I'm going to go back to more points on staleness here, when people know the lists things get taking for granted - a spawn is updated and it just becomes 'oh, this pokemon is no longer common here'. Why can't changes be more interesting? Having players not know this could allow us to make small tweaks to maps that change rarities for certian pokemon during summer, unique spawns on maps could appear and someone may stumble upon something new. It allows us the possibility to make the game more dynamic and give benefits to exploring maps looking for new pokemon or places as you could not just /list viridian forest and see that bulbasaur had been added and the watch everyone flock to the map for it. You could not /list secret area 2 and find that this whole map exsisted and had cool pokes. Maybe we added a new hidden map, what would be better - a) finding out it was there by seeing it on /list zubat or b) be casually walking through diglett cave and see a whole in the ground, dropping you into a new underground cave system?
Tl;Dr - Read it please, and really I want to see some decent arguments to why keeping the command is a good idea.