the nucleus of a European public ?
Lobbying - that is people talking about specific, sometimes even very specific issues no one else cares about. Probably not quite. The issues are from (or meant for) the political sytem. Decision-makers are the counterparts of lobbyists - which means there are two. If those two are sharing information and exchanging opinions about issue X, the conversations should be interesting for other actors. At least two kinds are certain to be more or less interested: 1. stakeholders in X; and 2. journalists who want to know more about X.
Discourse between politicians and lobbyists about issue X might than be regarded as some kind of a very low key quasi-public discourse - at least inasmuch X finds its way onto the political agenda or the journalist understands X and writes about it.
Might lobbying in Brussels than be seen as a low intensity and thinly populated European public?