I'm pretty sure the Shimano 5700 shifters I'm using will be available for a long time. Tiagra is still available in a triple as well.

If not, I guess I have to bite the bullet and go for a bigger cassette and live with the smallest small ring they can give me.

I have 26x30 now and I might not use the last two or three, but if I'm 120 miles into a brevet and my legs feel like jello, I will be happy to climb at 7 mph and finish.