This is all about a thought experiment :
Is there an hypothetical (or may it be real?) case of a stellar system, in which both methods of transit and radial velocities, are invalidated by some orbital configuration, providing a constant light dimming (each egress is perfectly compensated by an other planet ingress) and eccentricities and mass repartition of the planets around their star, make the barycenter of the entire system stay still at the center of the star.
I thought about a simple configuration of several similar planets sharing a single circular orbital path (see below). But are there any possibility for this to happen with multiple elliptical orbits, of different sizes & eccentricities? How likely is it to exist since the universe is quite big?