By the time you size the recirc loop and route the recirc loop to do heating as well as recirc, and then install a control system, you might just as well dedicate a heating loop with it's own circulator. It seems you might be adding too much complexity only to avoid using another circulator.
If you propose putting the heating loops in the joist bay space then the temp required is about the same as the recirc temp. So maybe you can avoid the diverters and simply let the recirc heat the floor. Of course, you'd have heat when you wanted hot water and you'd have it all year, but that might be fine. Heating tile from joist bay tubing is slow and requires a higher temp than tubing in a mortar bed or thin slab.