Yes, as you said the original model does not include sterile neutrinos, but it is a new approach for an potential explanation of dark matter.

To be honest, the model is one model among hundreds. It is, IMO, as appealing as many models, and thus not very unconventional.

More precisely, dark matter fermions are common to many models, scalar mediators too. However, having vector-like leptons is more special and thus interesting. However, interesting does not mean unconventional.

This model will definitely be considered (in particular by its authors) and confronted to future data. You can believe it :)