Exciting development. I really wish somebody would nail a commercially viable Thorium reactor but it seems there are real engineering complications around scaling molten salt reactors.
The great thing about boiling water reactors is that you just have to handle water. The radioactive portion of the systems is simple. Which is good, because it can't be maintained much during the entire lifespan of the plant.
When you look at the history of nuclear reactors, almost all the problems involve plumbing. The less that can go wrong with the plumbing, over 60 years or so, the better. For molten salt reactors, the physics is promising, the chemistry is a pain (fluorine, for starters), and the plumbing has major corrosion and clogging problems (high temperature radioactive molten salts and pipes just do not get along, even with really exotic alloys.)
It's not impossible. But it's going to be prone to expensive problems, some of which probably will not be anticipated. Remember Ft. St. Vrain, the helium gas cooled reactor. Great idea. Ran for ten years. Even used some thorium. Troubles in the radioactive portion of the gas plumbing system meant it had to be shut down and dismantled.[2] That was sad, because it actually worked well for years.
[1] https://www.osti.gov/servlets/purl/1484689
[2] https://en.wikipedia.org/wiki/Fort_Saint_Vrain_Nuclear_Power...
Online reprocessing of nuclear fuel necessary for some thorium fuel cycle designs (reprocessing inside the nuclear power plant) could increase the risk of nuclear proliferation. U.S. government, as a general policy, doesn't like when non-weapon states do nuclear reprocessing.
These days I am more excited about Plutonium cycle reactors using chloride salts because they fix the problems of the FBR (occupational safety in fuel fabrication for one) and the fluoride salt reactors (having to dispose of used graphite cores). You do get some longer lived TRUs but you have so many excess neutrons you could burn some of the fission products. Most important the Pu cycle can be launched with the nuclear waste we already have, whereas the math doesn’t really work for launching LFTR.
Moltex got around this in their concept by only using chloride salts inside the fuel tubes; the surrounding sterile molten salt was a fluoride. Being sterile, the oxidation potential of the fluoride salt could be kept low enough to be compatible with stainless steel.
(Moltex ran out of money last year, I've read, and has been selling its IP as distressed assets.)