The Senate is promising not to approve any nominations made by Obama. Good for them. They are a sack of liars, but let’s assume they are willing to hold to this one. Rubio wants to consolidate the non-Trump vote which is essentially split three ways between 1) Rubio 2) Cruz 3) Other.
You want Cruz’ support? Great – nominate him to the Supreme Court right now. I mean seriously, write up the paper and sign it contingent upon you becoming President. Sponsor a Senate bill with a binding resolution to hear the nomination and vote upon it in the time between the Presidential inauguration and when the next Congress is seated. You then promise Cruz supporters that he will be affecting court decisions for the next 40 years.
Seriously, do it. Refraining from doing so is part of why you cannot win Cruz supporters. We don’t believe you will nominate truly principled conservative jurists. Prove us wrong.