(I'm reading your post via Google Translate, so I apologize for any misunderstanding on my part).

It seems like some of these things are not real problems. Why does there need to be a centralized end-to-end system? Just issue the buys on the internal market and then whoever has access to public exchanges can arbitrage from them.

First of all, the Steemit Wallet market has a 24-hour trading volume of about $100, so it is not realistically usable, so let's pass.

Trading volumes are not some fixed quantity. If an account bankrolled by the DAO starts selling SBDs on the internal market the volume will go up. If nobody shows up to buy the SBDs the problem fixes itself, the account can just give the unsellable SBDs back to the DAO.