The drive system technology will very likely come courtesy of Toyota.
If Toyota and Honda are jumping in on this, then BMW feels it ought to as well. It actually makes perfect sense for the German carmaker to develop a hydrogen fuel cell car for a few reasons. The first is so that it can claim to be at the forefront of advanced automotive propulsion technologies. Secondly, BMW currently has a joint venture agreement with Toyota that'll help lower development costs for advanced alternative drive systems.
The BMW-Toyota sports car project is also very much in progress, but we're talking about hydrogen here, and its place in BMW's future plans. According to a report from Autocar, the German automaker is strongly considering a new i-branded model, potentially an i5, that'll utilize a revised version of the hydrogen-electric fuel cell system from the Toyota FCV. No launch timeframe was mentioned but based on existing market trends, we'd be willing to bet BMW is shifting this project into high gear. Doing so would add a certain technological prestige factor by having a pure EV (i3), a plug-in hybrid sports car (i8), and the hydrogen fuel cell i5.