it would be possible, yes. however, the pi is an end product in and of itself, and they are not accepting resale/redistribution offers from third parties in order to make sure the price stays where it is. that means that anyone who wanted to one would have to buy a pi as well as any other components on their own and put them together, which i doubt would be very popular. it would be much better to just go through with an OTcalc type idea and distribute finished products.
edit: furthermore, it wouldn't be cost-effective at all the pi, though small, is a complete personal computer on its own, with full hd video etcetera. there is absolutely no reason to pay $25 and have specs like that in a pocket graphing calculator (not to mention the added cost for a screen, keyboard, and case). just install your linux distro and CAS of choice and plug it into your tv =)