Is It True That Aer Lingus are soon going to be Flying Belfas-Shannon again?
Not gonna happen. As I've said before, the flight would have to be operated by SNN crews due to an agreement which prevents non-ROI based crews operating flights into ROI airports. This reason alone should put to rest any rumour that EI is planning to start a SNN/BFS route. EI neither have aircraft based at SNN which could operate the route, nor would want to, since SNN is a high cost base for EI.
There's never been a stand-alone service between Belfast and Shannon, and I don't think there ever will be.
So, to answer your question - no it's not true.