This is all very true but there is one thing you didn't factor into this reply; the equipment for the incineration has already been purchased and installed.
Shaker tables were originally introduced for use in mining where physical separation is not possible unless you have a river flowing through your claim.
The method of burning off whatever can be incinerated followed by treatment of the metal fraction has been the go to technology in the e-scrap recovery industry for years now. Likely because incineration has been around for many many years and the first e-scrap processors used what they had.
I think it would be a great test for someone set up to granulate and incinerate to split a lot and process half the typical way to quantify the values, and granulate and ball mill the second half and pass it over a table. You are absolutely correct about the minimized environmental impact and it has the potential to radically change the process.
Advanced planning is always wise but I don't see the table manufacturers trying to implement this technology very often. Back in the early 90's I generated a lot of processed sweeps from jewelry production which was incinerated, and milled to a -60 mesh. This was shipped off to Degussa, if I remember correctly, for processing. I had read about shaker tables and thought there was potential. The material I produced had a gold content as high as 1 ounce per pound. After discussing the feedstock with Action Mining Services, I was assured the equipment would work. I took a few pounds, hopped on a plane, and they had a table set up for me to have my sample run over. After it was processed the table could not separate the wheat from the chaff as it were. No gold remained on the table, it all passed off with the fines. To this day there is a huge market if this type of separation was effective for fine powders processed, as most refiners today ship these powders to Europe for smelting. If the tables worked there is a huge potential, huge. If any of the table experts here would be willing to work on this application I know a good number of refiners generating these powders and I could easily connect the interested parties. Huge potential! (not for me personally, I'm mostly retired and in the giving back mode)