Every tank takes credits, and there's two ways to deal with that:
(1) Be patient while you accumulate the necessary credits
(2) Use money to accumulate credits faster, whether with a premium vehicle, premium account, or both.
The unspoken implication in the OP's suggestion is that he doesn't want to do either, and thinks WG would be smart to fix it so he doesn't have to be patient but also doesn't have to pay WG a dime.
With the availability of premium rounds for credits, and the upcoming availability of premium consumables for credits, WG has effectively fixed it so that spending real money gives you no boost to performance, it merely reduces the amount of work you have to do for a given amount of credits and/or EXP:
• Premium tanks accumulate credits faster
• Premium accounts accumulate credits and EXP faster
• Spending gold on crew retraining merely saves you time and EXP expended on improving crew
• Spending gold to convert free EXP merely gets you more EXP that would effectively not exist otherwise
• Converting gold to credits (bad use of gold) lets you get more credits instantly
But none of these things, obviously, can ever be bought with credits, along with garage spaces. These are non-in-game advantages and are exactly what WG should be making their dollars on. Yet the OP and others think that WG should give people a way to sidestep these things and allow them to achieve the same effect without spending money.
If you want to accumulate credits, play middle tier tanks and/or don't suck.
If you want any of the above things, accept that:
• WG needs to make cash somewhere, and
• with the end of the last pay to win features (premium rounds and consumables for gold only) these are things WG will be making money from, so
• therefore you'll have to pay real money if you want these things.
Grind the credits. If they aren't accumulating fast enough then buy a premium tank and/or account. I used the Valentine's Day code yesterday, and I can tell you that my SP combined with a (brief) premium account was a serious credit-making combination.
But please stop thinking of newer and better ways for WG to give everything away for free.