Alright, the X-Men event in Marvel War of Heroes is looming right around the corner and I do have some possibly interesting news regarding it thanks to a commentator.
The Phoenix Force Card may in fact be the 1000-2500 boost card for the upcoming event. This would be acceptable lore wise, especially if they don't intent to release Xavier yet. If you go into SHIELD Enforcement Training and look up the rewards, click on Phoenix Force. You will notice in bright red above the card a message: New cards from famous artists! Have these cards ready for the upcoming Event! If you do the same for each of the other reward cards from SHIELD ET, you'll notice that none of them have this same message. As a result, I wouldn't suggest trading off your Phoenix Force just yet or you may wish you hadn't when her price goes up by 10-20PP.
Now, personally, I would much rather see Xavier released as the 1000-2500 card. If they do that I'm sure they'll release him mid event in card packs to earn some money.
**NOTE: Turns out phoenix wasn't the cards :( Lady Liberty She-Hulk and Precise Shot Hawkeye offered some weaker bonuses, but ended up being the event cards**
For more information on the event check out:
X-Men Raider Cards