I think a pool would be okay. I believe it is possible to keep the existing internal market and add a pool to it where as a taker you draw liquidity from both the pool and any open orders. Bitshares may have done this, or maybe I misunderstood what they did.

But, you know, development resources, priorities, etc. I don't think that many people think this is really a high priority. The existing internal market, centralized exchanges, and other DEX all work okay (not ideal, I agree).