Okay, let me see if I can explain it from the stance I have taken ... and I don't really agree with this (entrapment, reasons) :
Expansions players are already paying for the game and there is a shortage of people to team with.
Fr00bs may not be sure if they want to upgrade.
Then there is this "no RL$ cost way to see the shadowlands" and it is available as long as you can get enough credits for it.
You would be "sponsored" with a "club membership" by a paid account. Basically, they would be saying:
I have found a person I want to team with and I am willing to make a sacrifice to have them where I want them to team with them.
There would be no official RL$ <-> credit exchanges. (Sadly, black market sales of "vouching" would likely occur.)
When their zest for generating and sinking credits wanes, then they would be trapped with toons they care about on an account that needs $5 a month. Then they either leave, reroll on a fr00b, pay up or keep playing being in teams, keeping the paid players happy, while trying to generate enough credits.