First off this isn't a thread about me asking for classic servers. Financially and as a player I think they would be a waste for Blizzard to implement. But they are fun to think about.
Onto the topic, if Blizzard were to introduce some version of classic server/s what would you want them to be like?
1. Normal Servers
For me I would have starting off one normal server of each previous expansion. So one Vanilla, BC, etc. I would have them all progress at around the normal rate except all would be on the same time, around 2 years total for all. This would mean some would have a patches stretched out and other expansions would have some of the longer patches cut short. Also all patches with actual bugs, would be glossed over to the next patch immediately.
This ties into my second part of ideal system. After 2 years, you have the option to leave it on this server that will perpetually stay the same patch forever Lets call this server BC.a. Or transfer to the newly started server of the next expansion BC.a to the newly formed Wrath.b (Vanilla>BC, BC>Wrath, etc.)
Then the process starts all over again. Except this time if you want to stay in the same patch you transfer to BC.a so the most servers at any time for any expansion are two. The .a are stuck at the last patch forever, and the other is constantly recycling itself over and over either pushing characters to BC.a or Wrath.b. You can starting in vanilla progress all the way to whatever the current expansion at the time is after many 2 year cycles.
2. Fast Servers
Secondly I would implement 1, or however many they gauge people would want of "fast" servers. This would progress from vanilla all the way to the current patch then reset, with each expansion lasting ~6 months and raid lockouts being greatly reduced, but not removed. Once it hits the current patch you have to transfer to an existing realm, and the process starts again.
3. Race Realm
Finally I would have a.... "race realm". I have no idea if it is remotely possibly to implement or even something they would bother with. But I think it would be fun if there was a realm where you had to progress raid to raid, from vanilla all the way to highest progression of the current tier, doing the max possible hardness on all raids before. This would constantly update solely for you, or perhaps on a guild by guild basis. There would be no raid lockouts and this would be solely for guilds wanting to race or just see old content in a quickish fashion.
The kicker is, once you say hit whatever button tells blizzard to progress you to the next raid, you can never access the old raids again. Same for dungeons which would be the first tier of all expansions. So you have to adequately gear yourself before you move on and if you move on to early progress will be sluggish or impossible. Leveling, professions, etc would all be like normal which would add another factor to the whole race theme. This would be for the elite of the elite and would truly be an intense world first race to behold.
TLDR: 1, eventually 2 normal realms of each expansion. 1+ fast servers. 1 Race server.
This isn't for a debate on how good WOW is now or back then. Just talking about what type of alternate servers you would be interested in, with regards to them being of previous expansions.