I am kinda in the middle about this right now.
Good aspects: I do like that it would change things up for the game base and it could cause them to get more interested in this. Not only would it do this but it would create a new thrill because players won't just need to go into their enderchest to get the needed materials, they just need to figure that out. It shouldn't be too heavy of a work load for Ogar and dirt to put in so that shouldn't be an issue.
Issues I found with it: This would cause a lot of asking "what melts on calm/annoyed/angry" we still have players doing this an we have been around for a good while now. Not only this but then we would have to redo the tutorial (not hard I know but still). Aside from this the list we have made by would have to be scrapped and I don't particularly like that idea. The staffers would also have to relearn what melts on each mood and it would a while to do that.
All in all I am not really wanting something like this right now. Yes, it has its positive aspects but I think the negative ones I pointed out are a big problem and could cause many issues. I would however support a mood in which reversed blocks melt or something like "The Lava God is feeling random" in which random blocks melt. Detecting the blocks that melted in this case won't be hard because of /prism and it is more plausible in my opinion than that your suggestion.
I do like your suggestion Bram, I just don't think we can have it in here right now.