This is my first attempt at something difficult: finding the best players that aren’t regularly playing County Cricket, but that are good enough to do so. In theory there shouldn’t be very many players like this – because counties will know who their best players are.
I’ve used my database of bowling performances from 2016-19 in County Championship and 2nd XI Championship Cricket and picked out six that have promising data.
Time will tell how many of these players get regular first team cricket (and succeed) in 2020.

I’ve looked at players that have been selected for no more than three County Championship matches in 2019, for reasons other than injury.
Note that England’s Matt Parkinson only played four games for Lancashire in the 2019 County Championship, so might have made it onto a list like this, but he is unlikely to be under anyone’s radar now he’s in the Test squad.