Here are my thoughts for a CC:

1. No annual fee. Or if there is an annual fee offer a yearly bonus of 10k or so miles to make it worth it.

2. Make the points transferable to as many partners as possible especially airlines such as UA, US, BA, AF, AA and DL.

3. Ensure the transfers are instant.

4. Use visa/MC

5. Allow points to redeemed for gift cards.

For a FFP

1. Allow one way awards for half the miles.

2. Allow holds on awards for 3+ days.

3. Allow date and routing changes for free even after taking the outbound.

4. Stop the close in ticketing fee.

5. Allow alliance and non alliance partners to be mixed on one award.