Henry- there was an attempt at discussion of your important ILR article of January here – http://www.politicalworld.org/showthread.php?13600-quot-Structure-Democracy-and-the-Irish-Left-A-Call-for-Discussion-quot&highlight=Slate+System+socialist+party
The slate system, unless there is a short term reason for a party to adopt it as an emergency measure, is an expression of politics that is top down and lacks any confidence in the working class as a revolutionary class, or else that opposes social revolution. It is ant-dialectical, preventing the transformation into its opposite that is entailed in election of new leadership.
You are not going to get agreement on these things in a cross party grouping. If the existing parties of the Left are acting as a barrier to political development of the working class, and if that situation is entrenched through organisational and political blockages (like the SP “electoral” system) then a new organisation has to be formed.