This thread reminds me of this children's book...
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It seems like there was some sort of "Apple Derangement Syndrome" that developed with the introduction of the Apple Watch and continues on today. Symptoms: (a) feeling that a product is a failure because it isn't personally appealing enough to cause them to run out and buy it. (b) a feeling of doom created by purchasing a product that other people aren't falling over themselves to buy (c) a sense that a product will be discontinued because it doesn't sell in quantities surpassing all other Apple products.
The OP isn't the first to worry about the 12.9 Pro being discontinued. But it is puzzling. The 12.9 Pro sold more units in the final quarter of 2015 than the Surface Pro. Reviews have been overwhelmingly positive but more importantly, anecdotal reports from actual customers show an even greater reception.
The 12.9 Pro is not a niche product. The user experience just gets better and better as apps are improved to take advantage of the new form-factor. I'm not alone in having high hopes and expectations that during the WWDC this June that "The Empire Strike Backs" with some new stuff that will make the 12.9 Pro even more appealing.