No, that is a terrible idea. Frontier should simply balance their game to be rewarding to play. Mission payouts are currently all over the place and many missions are riddled with bugs, but sidestepping the issue by selling credits in the store doesn’t solve anything.
The OP’s sentiment has merit, and it’s not hard to understand why someone might feel that way about the game today. I wish I could understand why everytime Frontier fixes one bug they create another somewhere else. The updates often feel like Frontier is playing Wack-a-Mole with the bug reports. The game code must truly be a mess, or they just don’t have sufficient controls in place for a project this large. It’s frustrating for us players, but man it must be really frustrating for the devs too.
It;s not a 'terrible' idea, it's just a potential answer, and moreover, to one of the most important problems this game faces, retention of players who are not used to the MONUMENTAL level of grind and slow progress that Elite represents. If I had said 'allow people to buy Fed or Emp rank', or 'allow people to buy engineer unlocks' or 'allow people to buy Elite ranks', I'd expect a huge and justified backlash, but CREDITS AREN'T CONTENT, they are merely an enabler.
If you sit and think about what other game is closest to Elite in its gameplay, you have to really look at Grand Theft Auto. Look at how the online thrives in that game by offering choice (in terms of buying game content).