Hm, well, from speculations, I see people are very excited about the possible totally new mechanics to evolve old pokemon, but, what about the possibility that maybe it's also likely to presume that GF uses already "used" methods? For example, trading with Metal Coat or getting evolution while leveling up with AncientPower attack and so on. And in a way, I find it that way more reliable to discuss which pokemon are possible to get (pre)evo. Yes, I know, technically "all" of the pokemon can evolve excluding legendary and those which have already 3 stages, or hmmm, maybe can they add 4th stage evos? Yes, I see it unlikely, but...
When thinking this way, I find it easier to figure out possible solutions and so on. Like, say: Pinsir/Marowak/Farfetch'd? I'd see it likely to get evo in a way. I dunno, I find it hard to see those mons evolve "naturally" while just leveling up. I can in a contrary figure them quite clearly to evolve with help of Metal Coat to something which is, well., coated in metal! Then also I can imagine them having some ancient-form evo with help of AncientPower, although Marowak is only one of those I mentioned which have possibility to learn it.
Also, knowing GF they love to introduce "side-evolutions" for already existing Pokemon (dissapointing community usually, for not giving evo for mons which should've deserved it). Talking one's like Bellossom/Frosslass and so on. Is there pokemon you think could fit in this category that GF could consider using for new side-evolutions?
I'm just saying an idea about maybe possible speculations about a Relicanth evo, I found it some time ago that maybe it can be very plausible that it'd evolve. Not naturally of course because of its whole idea. I thought that "Maybe in next generation they'd have some scientists which have been studying this extraordinary creature, and found out that in some special way (like the aforementioned Metal Coat, AncientPower and so on...) it'd evolve!" I thought Relicanth evolving into some Water/Steel would be awesome. Empoleon sort of satisfied my thoughts in IV Gen at that time, but oh well.
I'm trying to say, that when we think that how'd GF let some Pokemon evolve after many generations, I see it very unlikely it'd do it "naturally". Why would them suddenly evolve without any assistance in a way? Evolution in real life isn't so terribly fast you know. In certain aspects, yes, but oh well. Nowadays it is we humans which speed it up artificially, directly or in-directly.
Maybe this way we can figure out easier which are more likely to evolve, although those might not be those Pokemon which community anticipate to evolve... Does some certain suggested Pokemon have in their real life counterparts some ancient, well-known, "stronger" versions? Or are there some pokemon which seem very appropriate and kind of "cool" (In childrens eyes at least) with new armour-like thing? And yeah, I know all the other stone/happiness/place based methods... I just don't mention examples about them, to keep this simple. Do you find some older pokemon "very likely" to evolve to darker form with Dusk Stone or more divine form with Shiny Stone?