Does the CCM Market Model only allocate between stock and bond ETFs?

No, the market model allocates between growth-oriented assets and conservative assets. Growth-oriented assets include, but are not limited to, stocks, sectors, regions of the globe, countries, commodity baskets, individual commodities, and precious metals. Conservative assets include, but are not limited to, bonds, currencies, precious metals, money markets, and cash. There are periods in history, such as 1994, when stocks and bonds drop in unison; thus, a model limited to just stocks and bonds can run into trouble. The model can "short" under very limited and specific conditions; more on shorting here.