there is no way around it, credits are broken and there is only one solution: fix and balance first, then a wipe. don't expect that happening.
Look at that, my favourite (but maybe dead) horse!
Yes, here's the big issue that needs to be understood when discussing an idea like materials for credits. Obviously it makes a lot of sense that materials, just like commodities, should be possible to trade for credits. There is no strange law of nature or legal structure in the Elite universe that would prevent us from doing this. But with the insanely broken credit economy we have, implementing a features like this will just move the taints from the credit economy to the material economy. I think that Frontier has good reason not to do something like this until the underlying problem is fixed.
This game has a very strange relationship to grind. Sometimes you can get ultrafast progression if you follow the right meta and play according to the rules and some times you are basically timewalled - it's 20 hours of gameplay to proceed, no matter user skill, how much risk they are willing to take or what approach they have. I don't like grind. I also don't think that this game should be a sandbox mode experience where you can gain everything practically immediatly. The real (and difficult) solution in my opinion is to make the basic game experience meaningful and have progression being something that happens on the side. What's meaningful, of course, differs between people. I think that features that would make the game meaningful to me would be more challenge and variation from the surroundings (stronger NPC, more NPC character archetypes, more complex and difficult missions, more basic 'scenarios' if that makes sense), a working economy (where it feels like commodities actually partake directly in production chains, and rewards scale with risk and investment) and a general feeling of a 'living' universe (numerous things connected to how factions work, news, ingame events, background lore and even things like system/planet/station names and system flavour descriptions). Oh, and more engaging multiplayer gameplay, PvP needs to feel better. Commodity prices and player bounties have pretty much not scaled at all despite the
massive inflation that the credit economy has undergone since the beta.
Another interesting approach could be to drastically reduce the permamence of all assets. In a game like DayZ, one sniper or 3 seconds of disorientation can be enough for you to lose everything and start over from the beginning. Then, it does not matter much that you, with some luck or taking a few risks, can get well on the way back to the top in a short time. I'm not suggesting this for Elite, I just wanted to bring it up as another approach to try and shed some light on what I think this problem looks like.
Instead of fixing this (to be fair, complex, difficult and of subjective nature) problem, we have frontier introducing new ''currencies'' (can they even be called that when they are not interchangeable with the other currencies and only substitutable for a very narrow category of goods/services?). Congratulations! The grind is saved, by compartmentalizing the game economy. Ultimately I think that it would be better to attack the big underlying problems, but you can't put a name on that and sell it as DLC...