Sounds like a plan. If the elected PM could only choose his cabinet from such a group & not from the ranks of his own party in the Commons, then the function of the Commons would be to hold the Executive to account, not to hope to join it as at present.

There are similarities with the American system here, which unfortunately hasn't turned out to be the greatest, so mucho thought will have to go into getting the detail right.

I don't think ideas such as these will gain traction in our lifetime though. A pity.