I would wager more appearances like this will happen in the Arrow-verse in general, especially with the 20 year gap that takes place between Arrow and the Mia Smoak-centered spinoff, assuming that gets a series order.
Ideally, The Flash can be one of those shows that checks in with key characters of the spinoff.
David Ramsey appearing on The Flash post-Arrow is exciting, and certainly leaves the door open for more former Arrow stars to appear in the future.