Are 32-bit controllers like Due the future of Arduino?Of course! But also, it depends on the project.
A lot of exciting new possibilities derive from the use of a 32-bit architecture.
Nevertheless, if your project is not very demanding in terms of computational resources, 8-bit would be probably the right choice (in terms of energy efficiency, chip costs, ...).
All in all, the future to me is that you have a bunch of different architectures bit-wise so that you can choose the one that fits your computational and IO needs.