This is a strong possibility. For all we know at this point, those phone calls may not be directly referencing anything to discover in the game, but rather highlighting mechanics introduced in the demo that will be fully realized in Resident Evil 7. Memories would be the VHS - using other tapes found in the full house to change the game. Power is choice - witnessing the game change based on the choices we make. Goodbye - well... I don't really know. Either way, it makes sense for these endings to be the only endings.
Then again, we did have the rep that said we could beat the game and get outside. He could have just been adding fuel to the fire though, since no other rep seemed to be as willing to speak on the subject as him.
If they retain the VHS mechanic then the memories hold the clues comment and power to choose comment fit perfectly, demonstrated by picking the lock in the VHS to gain access to the axe in current time, i imagine the final game will have a lot of time related puzzles like that where choosing to stop the tape at a certain point also plays a part too.
But personally, how I read the three phone messages is as such:
Memories hold the clues - Reference to being able to change the present with actions done in VHS and memorizing minor changes in past vs present situations.
Power to choose - Ability to stop the tape or continue, Example: you don't actually need to completely watch the tape to obtain the axe, if you exit the tape after unlocking the drawer and opening it, you can then access the axe without watching Andre die.
Have to say goodbye eventually - Reference to having to completely watch the tape at some point in order to accomplish certain goals - in the demos case, obtaining the back door key.