Here's what I wrote on the Guardian Politics Blog earlier today:
In my view we should go further, and make it possible for people to answer questions in the Commons without needing to be a member of either House of Parliament. This would achieve two things. Firstly, it would enable Prime Ministers to appoint the very best people to their Cabinets without them needing to become MPs or peers. Secondly, it would move us closer to the classic Separation of Powers doctrine on which the US constitution is built. The Prime Minister would continue to be the person who can command a majority in the House of Commons, and would thus invariably be an MP. But he would be able to appoint anyone he liked to his Cabinet in the knowledge that they remained accountable to Parliament through parliamentary questions and (more powerful) select committees.
To see the whole discussion in context, see Andrew Sparrow's original blogpost here.