From the info on Legendary Ring upgrades, and the new information from the latest Hazzikostas interview:

Most players should be able to collect all of the Tome of Chaos in a month or so.
Vanion's interview confirmed that Archimonde will drop Crystallized Fel on Normal or greater difficulty, allowing you to upgrade your ring's stats and proc to item level 795, gaining 3 item levels each time. You can only get one per week, so it will take 20 weeks to hit 795.
Assuming you are getting the Ring in 4 to 6 weeks and start killing Archimonde on Normal+, you then will need 20 weeks to upgrade it to the max iLvl. Assuming further that Blizzard does not intend for you to skip the "content" (which is a rock solid assumption) and that they correctly planned the drop rate and iLvl increase size (which is admittedly a much weaker assumption), you are looking for at least 24 to 26 weeks of 6.2.x, which means that in January 2016 you will most likely still be farming Apexis in Tanaan, sending your ships & followers to the facebook missions and raiding Hellfire Citadel.


But hey, Ashran/Flying/Pet battles/Garrison invasions/Timewalking weekends will surely make it worth your subscription money.

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Corroborative evidence:
Wow PvP seasons usually last > 22 weeks. PvP season 2 starts 01.07

Also, the length of modern beta is ~ 6 months (26 weeks) so unless you'll hear the (closed) beta announcement in a month don't bet on WoD ending with 6.2.
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