nvm mods can delete this thread
user @Xar226 pointed out the flaws and he is right:
$25/month is very unlikely to happen. The furthest I could see it stretching would be to Netflix levels, which is about $15/mo near the top I believe. Meaning essentially that for WOW players, it's free.
Overwatch launched with 7 million units sold in the first week at $39.99 = $279.3million. To make this a financially justifiable decision based on that game alone this service would need to bring 3.1 million new subscribers (people who wouldn't have subscribed otherwise) and they each would need to stay 6 months. Just to make up for the revenue of that single game launch over its first week. (Since you threw out $25/mo, even though I think that's unrealistic it would be 1.8 million subscribers who stay six months.) That's not counting the fact that they're basically losing all the revenue from current WOW subscribers since it would now just be a free feature to this new subscription.
If they believe that would increase other factors (paid services, loot box sales, etc) and attract enough non-WOW players to pay for development and maintenance of both WOW (now covered under the same umbrella) and other properties, it's not impossible. But if you're asking me? I don't see it happening. They'd lose too much money if they're at a price point people would actually want to pay and get too few subscribers if they're at a point where it makes financial sense. Heck, I'm not even sure $25 makes financial sense for either party.