An alternative
opinion/proposal, also while getting rid of phasing (
aka individual visual progress of location, leaving it be server based)... and at the same time together with direct "constant" scaling (scaling is not necessary if each of expansions has adequately distributed levels' ranking (type of... first 10 levels are always starting location, and then you go by expansion's choice) that allows you to reach necessary, taken as maximum, point, also, in absence of system assuming/based on phasing, changing expansions in the process, with special desire, will be absolutely painless;
scaling is always bad, it's censor's constant). In other words - no auto teleports/"motionless"-dungeons'spam, but they're always available "with your feet" (even if you have to go through part of location with mobs that are quite dangerous for a lone traveler, or already easier with automatically suggested "set" of fellow travelers), albeit not with entire volume of
quests that can be "taken out of somewhere" due to direct and adequate organization of quests/lvling (without utilitarian
degenerate simplification mechanisms).
Considering all of above, there won't need to be
afraid of "between expansions" problems availability of dungeons and their level requirements. In fact, most of work they have
done recently, if not
worsened situation,
then at least was useless.
How about that, huh?
*barely audible recalls with unkind word this organization in Cata*