The hydrolysing of low grade oil is part of many government reports on possible ways forward, and the disturbing thing I found was that it was mention especially in conjunction with nuclear electricity, essentially negating the good environmental effect of it. Though reports and suggestions are still far away from what will actually take place, and I suggest as you mention that the oil industry is one of the biggest backers of these ideas, the fact that they are still there is enough to be concerned in my mind, especially in a brutally oil/gasoline dependant country as US.
The monju incident was only a small leak of secondary non-irradiated sodium if I'm not missinformed, the eye opener which shut them down for so long was that it could happen, and a big sodium leak would present huge challenges with safety from the sodium, in addition to the reactor-problem of loss of heat sink, and if you focus on the sodium only not dealing with possible problems in transport of core-heat etc, that is a big possible issue. lead-bismuth mixtures etc could be a solution to them as you mention. The interest in Japan about fast reactors had declined quite much from what I was told when I was there this summer, talking to some in the nuclear research, possibly due to the difficulties getting running/funding from the authorities/agencies. But they are as you mentioned supposed to be allowed to run again after more than a decade of standstill.
I would oppose to the main reason against H2 infrastructure being the electricity cost, it have technical challenges too, especially transport and storage in tanks etc associated with propulsion. High cost of electricity should promote hydrogen (from water of course, not the oil-alternative) since you don't want to waste any energy. It anit fully as easy as that, but high temperature reactors or plants could hydrolyse water with heat instead of directly using lots of electricity even if you need to compress it in a costly manner afterwards. But a H2 infrastructure is nowhere near to be realized from what I've seen of US and all european countries. The use of IFR to desalinate water is a good one, but nearly 100% of it is done with fossile energy atm, and only the kazaks have any decent experience with nuclear desalination (30-40 years running), and it would not be limited to necessarily IFRs so I can't see it as a good argument for the IFR, rather than for nuclear plants in general.
As for the long life of normal light water waste and the long life, you are neglecting reprocessing and MOX, vitrification, which is very much a reality in much of the world (not in my country though similarly to US), which reduces the bulk, and changes the times substatntially. Also if talking about using the light water waste in IFRs then that issue is not there anymore, although that certainly is a strong argument for the IFR, but also for some other reactors/reprocessings.