Very extensive devolution to the very local level, Jewish or Arab, religious or secular, Muslim or Christian, et cetera. Three parliamentary chambers, each about one third the size of the present one, namely one for the Haredim, one for the Arabs, and one for everyone else.
All legislation to require the approval of all three chambers. Each chamber to elect a Co-President, all three of whom would have to approve all legislation and senior appointments. Each chamber to be guaranteed a Minister in each department and at least a quarter of Cabinet posts. Yiddish to be recognised, as the quid pro quo for recognising all those villages in the Galilee and the Negev.
The alliance necessary to pull this off would take an awful lot of effort. But two peoples facing nothing less than denaturalisation could very well be prepared to make that amount of effort. The other lot should have had more children, or bothered to move there from places like London and New York. But they didn't.