Any export order is welcome be it 18 or 36. It's a evolving platform. Malaysia wants support infrastructure as well, once they see it is more affordable and easier to maintain they could possibly order more, or become regional support center for possible other clients.
These numbers suite Pakistan well at the moment because any larger numbers will mean need to create a alternate assembly line making the transaction more complex.
The JF-17 fulfills such a niche that I forsee it's future variants will be in production for a long long time, same as Super Mushak which still fetches orders because it offers good value for money. There aren't many new alternatives in the affordable supersonic light multi role category. Grippen is no longer a affordable light fighter, used F-16s will eventually become non feasible to new users and YAK-130 type jets are essentially high end trainers modded for combat. No comments for Tejas.
