if geula is based on level of observance and affiliation with torah judaism, in order to make up 20% you would probably have to include all denominations of orthodox jews and a large portion of conservative jews and some reform jews as well.
Take the US as a base. Eliminate 10% of the jewish people in the united states who are jewish but do not know it because their mother was completely unaffiliated. Eliminate another 30% or so atheist american jews and youre at 40%. Eliminate another 20% of jews that are not atheists but not affiliated with any synagogue or organized religion and inter-married jews and youre at 60%. Now eliminate the 20% most extreme non-observant jews of the reform movement and conservative movement and youre at 80%.
i am not sure that the other jews would even be interested in joining a jewish people in the middle east living by jewish standards.