Behind the scenes (aka future according to Toyota. OMG these people are visionary!!! )
"...to put it simply we just love engines."
Something standing out to me from that is that, for Toyota, they see this as a way of protecting jobs. Which sounds very altruistic, but it's also a company where one of their industry leading assets is under threat. They will naturally want to do all they can to maximise that asset, and throwing it out without investigating all options for it wouldn't be in keeping with that. There's a strong element of risk management here, as well as an eye on future profits for the company.
(I'm not exactly sure I'd describe that as visionary but that's me)
It's also the case that Japan has made far more distinct and strides to develop into a hydrogen economy and done so earlier than other nations/regions. It therefore makes a lot of sense that Toyota is tapping into that wider strategy with this initiative as a means to see what they can do with the ICE in future. Having said that, the base technology is not new and unique since BMW were also looking into it in the mid 2000s and the racing of the technology isn't new either, since Aston Martin raced a Rapide S converted to hydrogen at the Nürburgring 24 Hours in 2013. Neither projects yielded anything in terms of serious commercial offerings, but the surrounding conditions have changed significantly since then so it's far from a foregone conclusion that history will repeat itself.
Pretty cool that we got to see in that video where the hydrogen tanks were stored (6:24), which appear to be pretty beefy tanks taking up the entire back seat area. For a converted/prototype race car I don't think that's so much of an issue to be honest, but in this case it is an indication of both hydrogen's low volumetric energy density and a hydrogen combustion engine's low efficiency (20-25% compared to a fuel cell's ~60% are often quoted figures). You may be able to get 2-3 times more usable energy from the same amount of hydrogen by using a fuel cell, which is nothing to be sniffed at be it road or racetrack.
I'll only make the briefest of mentions that ~95% of global hydrogen production is from fossil fuels and produces CO2 as a by-product. That's because I think 'green' hydrogen production is now a strategic priority around the world and ties itself in nicely with a default transition to renewable energy and a zero-carbon energy grid. This can and will change over the next decade or two.
I honestly don't really disagree with Toyota at all in that broadening the options for zero-emissions is a good thing. What they're doing makes sense and, since developing hydrogen tanks and rapid refilling stations provides a common benefit to hydrogen fuel cells, racing/testing like this is by no means a waste of time even if the hydrogen ICE doesn't make it very far commercially. It's also hard to argue that having up to date research into what hydrogen fuelled ICEs are capable of is a bad thing - even having that in the back pocket in case it can be used as a solution somewhere at some time is a good thing to have in the face of a massive global transition to sustainability.
I'd agree with Toyota's expectations that ICE hydrogen will more likely offer some level of choice for future cars rather than being a universal solution. My expectation, based on current indications, would be that (for those in the world with the luxury of having a choice) this would be a choice made by car enthusiasts with a specific love of combustion engines rather than the average person choosing their daily drive. How big that future market will be is a massive unknown.