I'm not rejecting it solely because it supposedly attempts to find compromise, but because it's just a paper-thin idea. There would be controversy and claims of bias regarding the appointments to such a Citizens Assembly, the Brexiteers would generally dismiss it as yet another attempt to frustrate the will of the people and in the same vein, will question why the public need to be consulted again after a clear message was delivered in 2016.
It avoids the referendum campaign while not missing out on any of the other issues which come with a referendum. It's a solution to try and minimise further division and to try and increase engagement in the democratic process itself. One of the most damaging parts of this whole thing, which likes of Will Jennings are flagging up, is that our pretty much longterm stable attitude towards Parliament and politicians has collapsed since 2016. That's obviously ugly for a representative democracy. In any case, ideas of trying to minimise division are rapidly becoming moot, if they are not already, given Johnson's approach can only ramp things up further. Additionally, main reason that this sort of idea won't take off is, purely politically, there's no incentive to allow a compromise to be found now whether the WA gets passed at the last moment or not.