Probably more of a local supply chain issue, I've not seen any signs of a nationwide banana shortage yet. There is a fungal disease (a strain of fusarium wilt labeledTR4, also called Panama Disease) that will eventually wipe out most of the Cavendish banana plants, like an earlier strain, TR1, did with the Gros Michel in the 50's, but it will likely take another 10-20 years. I don't know if they've settled on a new variety to replace it, and it takes something like 5-10 years for a banana plantation to get fully productive banana plants from new stock.
There may be better mitigation efforts in place than in the 50's, since Gros Michel was wiped out quite quickly once TR1 was widespread, though TR4 has been around for over 30 years already. I've seen some reports of trying to breed fungal resistance into Cavendish, but since banana plants are mainly reproduced by cloning, that's not a very simple or quick strategy. Cloning is also the reason TR4 is a world-wide problem, just like it was for the Gros Michel.
About two years ago I read an article about using gene splicing to add fusarium resistance to the Cavendish banana from fusarium resistant tomatoes, but the anti-GMO folks were quick to pick up on that and I don't know if that project is still ongoing.
The 1920's Broadway tune "Yes we have no bananas" was written about banana shortages from the early years of the TR1 plague on the Gros Michel banana.
