Likud - Israel Our Home merger

In the latest political earthquake, Likud and Yisrael Beitenu (Israel Our Home) announced a mnerger for the upcoming elections. Some of the reports include a prime minister rotation where Natanyahu will head it for 3 years and Lieberman for the remaining 1.  Of course there has never been a Knesset that actually lasted the full 4 years, so Lieberman would get screwed in that scenario.

What's puzzling to me is who gains by this move. Looking at the political landscape, I don't see anybody who was going to vote for another party change their minds and vote for this one. But I do see Likudniks who don't like Lieberman and YB people who think Lieberman is selling them out leaving the party. In other words, I see Lapid or other "centrist" party gaining a seat or 2 and the Bayit Yehudi gaining a seat or 2.

What could be happening behind the scenes is a consolidation in preparation for a "change in style of government" law that passes shortly before the government disbands. This law, which everyone has been talking about for a decade would change the minimum number of seats for a party to 10. That would completely wipe out the smaller parties and there is enough support for that kind of law among the big parties right now. Currently, the minimum number of seats for a party in the Knesset is 3. In a coalition agreement, that gives 2.5% of the seats the power to impose their will on the majority. A 10 seat law would completely get rid of the fringe parties and force unity and compromise amongst people who stand on "principles."

In fact, I can see only good coming from a minimum 10 seat law.

---UPDATE---
I just heard an interesting take on the merger. In the last election, Kadima had the biggest party so they got the first chance to try and form a government. The Likud with YB together have the best chance of being the largest party and then having first chance to make a coalition.
Personally, I still don't think it is good for them.