How many people would return to Catholicism if the church becomes universalist(everyone is stated, by the clergy, to receive eternal salvation)? Why? How?
I think that - very likely - Paul Kuei-chi Tseng's contribution ("no comment") is the wisest one, given the nature of the question - but (foolishly), I would add the following:
Why could there be even any hypothetical benefit in the Catholic church becoming universalist? There are plenty of other religious or semi-religious bodies which adopt such a position, and the people who join them do so because they don't like the idea of a righteous deity who might possibly have something to say, judicially, about human sin.