If done at least semi-officially it could equally be a way to bring back lapsed players as much as any splitting of user base. Many leave in major updates or exciting new releases. WoW lost loads since LK. In other games LotRO horse riding update lost 30% of the users. GW2 redesigned for the intellectually challenged. I'm sure some would want to come back to the game before it was wrecked. Maybe not so much GW2 - it was always too easy to hold interest for long.
The problem I see is old versions would be unlikely to get updates like new content or dungeons so even those hoping to play long term would get bored eventually.
Still to put WOW in perspective with other games you list, WOW's population loss and gains around expansions tends to be higher in number than other games ever achieve.
Games age and taste change too. Blizzard has done an amazing job to see so many millions of players interested. The one surprise to me is how low of level their free play is limited to.
Oh very true. Somehow they made it achieve the same as most of the rest of the MMO space together. Never quite saw why as, well, I never got hooked on it, so left early. One of the kids is still hooked on WOW and won't let us kill the sub even now!
The problem I see is old versions would be unlikely to get updates like new content or dungeons so even those hoping to play long term would get bored eventually.