Walla has published the draft of a letter being prepared for signature by the gedolim, already signed by Rav Chaim Kanievsky, Rav Shalom Cohen and Rav Shalom Baadani, with more expected to add their signatures.

The letter calls for a cherem against any city rav who gives kashrut certification in another city in which he does not serve. Any rav that violates this order will be banned completely and his kashrut certification rejected. 

source: Walla News, Haredim10, Hamechadesh

1. In other words, the people who never supported eating from the Rabbanut hechsher, will also not support eating from the replacement to the Rabbanut hechsher. And the city rabbis that do not give hechsher in other cities - the Haredi rabbonim will recommend eating from their hechsher?

2. Interestingly, the Haredi rabbonim have no problem with the Haredi rabbonmi and hechshers giving kashrut certification in other cities. For examples - Rav Rubin gives hechshers all over the country. Rav Landau gives hechshers outside Bnei Braq (though not so much). The Eida gives hechshers outside Jerusalem. Kehilos gives hechshers outside Jerusalem and Bnei Braq. Nobody is boycotting them for this. It is only the "Zionist" (by Zionist I mean what would be called the State hechshers if not for the fact that it isnt the Rabbanut, but it is their replacement. Not exactly sure what to call it) hechshers and rabbis that are being banned from crossing city lines to certify kashrut - and ironically a good portion of the city rabbis are Haredi appointed by Shas. The point is though that the Haredi hechshers and rabbis do this all the time all over the country, but the Rabbanut-replacement hechshers wont be allowed to.