Earlier quoted context omitted.
My personal intuition is that splitting your userbase like this is disastrous for a game in the long-term (to say nothing of my intuition that 90% of people longing for "the old days" are just looking for a quick hit of nostalgia, with no intent to pay long-term). However, it's worth mentioning that Runescape now officially offers a "classic" version of the game alongside (and separate from) the modern version, which…
You know that is an argument about expansions in the first place? Significant player dropoffs in WoW happen in the last patches before new expansions. The userbase usually spikes up on new releases, but almost always drops lower every time, predominately because new releases gate players who were on old versions against those on the new one. Friends stop being interested, unsub, and never come back because the player…
It's pretty simple to avoid the problem of having players scattered across multiple content sets and levelcaps: stop bleeding your players dry. What are subscription fees paying for if not ongoing development of additional content?
IMO you should either charge for expansions or charge subscription fees - but not both.