The same thing that would happen if he were to enact into law any Halacha, say, required all of Israel to separate Terumah and Maaser.
What would happen in either with slavery or with Terumah and Maaser is that the frum Yidden would be very happy and celebrate whereas the westernized non-frum Israelis would be angry and protest.
And since there unfortunately are more non-frum than frum, Bibi being the political animal he is will do the politically expediant thing and not enact the halachicly correct law.