On topic, the levelling experience i had in Elysium tainted my enjoyment in vanilla.
I think some of you are missing the point, the question isn't how many modern servers and/or bandwidth actually support. For me, and apparently others, the question is after how many the servers just feel too crowded and have a negative impact in you gaming experience. I don't want to run around in Redshires with 500 other players levelling, the game wasn't designed with that in mind, the resources, the npcs, the spawned quest items were designed to have less ppl than that, at least i feel that way.
And having started a new char on Anathema a few weeks ago has only strenghtened this belief i have, it has been way more pleasing, you still have several folks in your lvl range (a few more wouldnt hurt thought) and the gaming experience has just been better overall.
A solution for this? In my eyes it would be to cap servers at a number around 3-4k, this way also allowing population to ballance evenly throughout the available realms.
Just my 2 cents.