I think Rubio is electable. You heard it here first
I think he is too. I think he is the GOP's best shot at this point, but sadly, the conservative constituents seem to mostly favor Trump, or Cruz. I hate to say it, but it's all setting up to be another Clinton win. However, a lot can change between now and November.
If Clinton makes it to the convention and has enough delegates for the nomination, Sanders will give the DNC a middle finger and run as an Independent. This will split the vote and put the Republican nominee in the WH. Now Bloomberg is making noise he may jump in as an Independent will further dilute the vote for the democrats.
The other scenario is Hillary doesn't make it, the convention happens and the DNC (in desperation) drafts Biden. Then Bernie does his thing and Bloomberg jumps in as well.
The DNC is facing a long uphill battle this time. They pinned their hopes on HRC and presumed it to be her coronation. Little did they realize (a) The public is sick and tired of "establishment" politicians, and (b) The appeal of "outsiders" to the voting public.