Could there be any other radionuclides in universe which are yet tobe discovered ?

That presupposes the ability of stars in their supernova state to cook higher & higher atomic-numbered elements, packing more and more binding energy against a tendency to fission.

Stability of Nuleus as the number of nucleons increases is complex & there seems to be no upper limit but an asymptotic tendency. The end is not yet in the vicinity. But, any such discovery of a new element or its isolation or artificial manufacture might be of academic interest only.

Very unlikely that there are any nuclides we have not yet seen but yet are stable enough to hang around and be detected. There's talk of an "island of stability" off the far top right of the chart but by "stable" they probably mean microseconds half-life not years.

I believe that particle accelerators are already at an energy that surpasses any supernovae, closing in on the energy densities that existed in the few seconds after the big bang. On the other hand, accelerator time is expensive and searching for unknown isotopes in the outfield is kind of a niche activity compared to trying to understand the existing isotope distribution or searching for Higgs.

It is unlikely. We have been able to produce most nuclides that can be produced without requiring extraordinarily high energy conditions.

Of course, the model of the atom and why it stays together could be wrong, but that does not seem to be the case. Nevertheless, "impossible" is hard to prove.

Yes, they just found one on Zogg-3, ready to hatch... look..!