here are my suggestions that are not on tentative lists:
I particularly liked
b. Laas Gaal
One certainly wonders why some of them have never previously been nominated or at least placed on a T List.
We have visited 26 of the 48 T List and 23 of the 43 Non T List sites on your list so can comment on some of them from first hand experience - concentrating on a few from the "Non T List" list!
a. Bonampak – I understand that the murals are considered particularly important but when I was there back in 1971 (!!) they were hardly visible among the undergrowth - no roads (we flew in), no other tourists and we stayed with the Lacandons in a nearby village. I guess they could be enough to raise it above the many other uninscribed Mayan sites?
b. Richat Structure - A bit difficult to make out "on the ground" even though the photos from space are spectacular. Given that it is generally agreed nowadays to be an eroded "dome" rather than a meteorite crater I wonder how "special" it is geologically other than for its amazing "regularity".
c. Panama and Suez Canals are certainly testimony to the engineering skills of their age and have great historical significance but they are both "working" canals and not really suitable for WHS inscription. For the Panama Canal however I do wonder if there might be some associated historic buildings which would be worth preserving as proxies for the canals themselves. I think particularly of the Admin building in Panama, some of the Canal Zone "colonial" areas and a Lock "control" building?
d. Tula. Certainly well worth a visit and represents a phase between the 2 "nearby" sites of Teotihuacan and Tenochtitlan so has the potentiall merit of filling a gap. Is also reasonably "Iconic" with its platform of statues!
e. Atomium - very much of its "era" with all that post WWII "hope" in technology/science- but, architecturally, is it really of any significance?
f. Kruger. Its best argument could be as part of a Transboundary park with Mozambique and Zimbabwe? I suspect that, ecologically, it doesn't add a lot to what is already inscribed
g. Royal Palace Bangkok - the unwillingness of the Thai government to progress a site in Bangkok is surprising. I would have thought it could succeed if they tried but it wouldn't be among my "top 50 missing"
h. The Matterhorn (Cervin). Certainly an impressive mountain but a lot of the Alps are already inscribed!
i. Palace of the Winds. Iconic building but surprisingly small and "lost" within surrounding Jaipur. I suppose that sites like Bremen town Hall "overcame" this weakness?
j. Brandenburg Gate . I personally can't see any reason for inscribing it let alone placing it in a Top 50 missing
k. Neuschwanstein. We have discussed this in this Forum previously. "Iconic"- certainly, but, as a 19th C artefact, what of real OUV does it demonstrate?
Re Perm-36 I note several comments on the Web that it is being "considered" for WH nomination – but I can never find anything specific.