I have the LEGO Boost kit, and I'm wondering if I can control it directly using the Powered Up app rather than programming it using the Boost app. Is this possible?
As of August 2018, this is not possible. However, TLG has stated that they plan to add more compatibility to the Powered Up system, and this will likely be available as a firmware update in the future:
Q. Will all different Powered Up components (Boost, WeDo, Train, etc) be able to communicate and control each other, e.g. running a Boost program sequence using a Powered Up hub or using sensors with Powered Up hubs?
A. It is the aim that the Powered UP platform will work together across both with the wired and wireless connection. Some of these connections are not implemented yet and will come through firmware and app updates.