Patch 9.5: Azeroth's Recovery
Non-warmode phased characters and new characters start in the old world *classic* pre-catactlysm and pre-BFA. (Also allowing anti-warmode phase to include Darnasus / Undercity unburned, opposed to using an NPC phaser.) They level moderatly slow (similar to classic) untill 60, while enjoying the ability to use dungeon and battleground finder but at a noted much lower experience gain compared to questing.
Every level from 10-60 grants a point from the old talent tree system, now called "Hero Talents". At 60 players gain their frist choice from the new (3 option MoP) talent system, now called "Power Talents". Also, PvP talents are all unlocked from level one and also usable anywhere even outside Warmode, now called "Battle Talents"
Players who reach level 60 are then able to enjoy classic raiding scaled at 25-40. Apon reaching level 60 players are labled as Contenders, allowing them to enable warmode which enters the world phased as post cataclysm / BFA. Epic Battlegrounds will be removed and rather will become part of the Warfronts (now unlocked at 60 and accable in SW / Org) allowing them to be participated in via an ongoing active war basis rather than a queue and have adopted a more classic battleground feel. These battles run the original honor rank 14 system.
The level cap will once again be level 60. Continuing to level in this matter will rather benefit your "Contender Level" At level 60 (Contender: Rank 1) the amount of "Contender Experience" you gain is increased. Every 10 levels beyond that resets their "Contnder Level" but grants a new "Contender Rank", a new Power Talent teir and another increases in the amount of "Contender Experience" they gain. Contender levels will unlocking new content. For example, at Contender: Rank 2 (10 contender levels from 60 *not chaning the actual players level from 60*) players again gain an increase in the amount of "Contender Experinece" they gain, get their second Power Talent choice and can queue or enter dungeons, raids and battlegrounds from the Burning Crusade. This will continue through the games progression making the current cap "Contender: Rank 8) allowing BFA content and the final Power Talent.
As you can see, the level cap would never change from 60, but Contender ranks unlock new content. This would greatly baseline the stats on gear allowing for all content to be relevent from 60. This would place PvP *Contender Rank gated* into 8 brackets (outside 1-59) and dungeons & raiding *not contender gated* into 1 bracket (outside difficulty)
As classic content ends, the classic client will disapear redirect its players and merge its realms into the current (BFA) client. Level 60 players would become Contenders. Level 120s becoming level 60s again but already having Contender Rank 8. This could be implimented using the "Contender Level" system. For example a level 92 character would become level 60 with Contender: Rank 4, level 2.