I have had this root sucker for years. The root stock is unknown, but I am preaty sure its mryobalan since the grafts are plums and the trunk looks like cherry. Question is do you think its to late in the season to cut it off and put it in a pot of its own?
Not too late as long as you can get a good amount of roots with the sucker. Try placing it is partial sun mostly shade until it fully adjusts. Below a pic of one my Myrobalan leaves for comparison. I pot suckers thru the growing season from some of My wild plums and never have one die.
its going to have over 1ft of root but that roots have been above ground particly coverd with dribris for 2 years is it still really root?
Most likely, try to get some active below ground roots, and scar the bark on the above ground apparent root down to the green cambium before you bury it. Should work. If you have rooting hormone use some on the scarred apparent root.