Don't get carried away. Nobody has said that KLM will begin flights to Belfast.
BBC reports that KLM plans to add three more UK airports to the 14 they already serve - and as there are not so many left that are not being served already Belfast obviously is in the drawing. How likely it is that Belfast is one of three will depend on how much an existing LCC link to AMS is seen as a nuisance by KLM - there are some other UK airports which lack such a competing LCC link to AMS (think of places like BOH, NQY, DSA, BLK).