Portfolio Diversification - Setting target weightings

It would be useful if in the Portfolio Diversification area we could set what our target weights should be and how far we have drifted from those values. We could then decide how to rebalance if we choose to and then assess the tax implications. Even better if we could do it with custom groups (e.g. US Large cap, US Small Cap, Ex-US International, Global Bonds, Commodities, REITs, etc)