Cutiefly
While we already have confirmation of an evolution for Cutiefly it still hasn't been revealed yet, I can say that it's evolution does greatly resemble the Hummingbird Moth...I believe the Riddler alluded to Cutielfy getting a three stage line (while this may or may not be true since he was incorrect with Type: Null's evolution although it's also possible that it was intentional since he's cryptic as ****) either way...My train of thought is, that Bug types for the most part when they have three stages, the middle stage is usually some sort of cacoon or pupa of some sort...Which could suggest that Cutiefly's evolution is actually it's Stage 2, while the middle stage may be a pupa of some kind...Although this would make more sense to me if Cutiefly wasn't a fly that evolved into a moth but rather a caterpillar...Larva, Pupa, Adult is the general lifecycle of most insects, not Adult, Pupa, Adult...Pokemon has for the most part referenced this fairly well in three stage evolutions for bug types (not so much in two stage)
I'm leaning towards Cutiefly only having two stages in it's evolutionary line with the Hummingbird Moth being it's only evolution...but then again anything can happen
Komala
I'm kinda getting a similar vibe to Slakoth for Komala...meaning it may evolve into something a bit more hyperactive and even possibly revert back into a sleepy state...but additionally Snorlax and Conkeldurr lines come to mind as well...Maybe Komala will evolve into a different kind of marsupial such as a Wombat or something or perhaps reference Australian aborigines, like if the log turns into a didgeridoo
Pikipek
It's fairly common for bird species to change between evolutions in Pokemon...Pidove beign a Pidgeon evolves into a Pheasant and Fletchling a Robin evolves into a Falcon, etc...However Pikipek is a pokemon who's characteristics as a Woodpecker can transfer well into larger stronger variations of other Woodpeckers...Woodpeckers themselves come in many different sizes and shapes...Pikipek seems more similar to the Pileated Woodpecker, going up from there it's evolution could reference the Ivory-billed Woodpecker or the Black Woodpecker, both of which are amoung the largest Woodpecker species, both also have simialr black bodies with red crests, although the Ivory billed retains the white colourations that Pikipek has...that said Pikipek's evolutions likely won't represent a specific species similar to Hoothoot and Noctowl...
Morellul
This one took a bit more digging as I'm not really a fungi expert...However Morellul appears to be based on the glow in the dark Mycena mushrooms which has dozens of different species it seems...really neat these things actually like something straight from an alien planet...
Morellull appears to have a gimmick centered around both illumination and spores (duh, since it's abilities are Illuminate and Effect Spore) but also as it's description suggests...There's quite a lot of potential and various different ways it can go, but I can see perhaps something akin to a mix of Vileplume and Weezing/Probopass in concept as it may turn into a larger Mushroom with smaller appendages that resemble other Morellul...
Perhaps the larger mushroom could resemble these Olearius?
I could also see it going through a three stage evolutionary family as well...It's second stage could be a two headed Morellul before becoming the larger shroom for it's final stage, like a mushroom version of the Magenzone line...
Passimian
Once again the Riddler suggests an evolution/prevolution for Passimian (as well as Oranguru)...For Passimian, if it would get another stage I feel like it would be a prevolution...Being a Lemur, which are mainly found in Madagascar I can see it's baby form being a literal Bush Baby, which are small primates that more resemble mice than monkeys and lemurs, it would seem the appropriate transition, especially if they give it a little berry to play with...perhaps as a means to train itself until it becomes a Passimian
Oranguru
Oranguru's appearance suggests a more mature individual, larger dominant males tend to have these large inflated fleshy cheeks which Oranguru's design seems to reference...It also has a more laidback and spiritual pose representing more of a Shaman, a guru, the village elder...I can see a possible prevolution of a more naive younger orangutan, possibly focused more on arboreal acrobatics (which Orangutan's are surprisingly really good at) or some form of martial arts...Perhaps an evolution of a Normal/Fighting into a Normal/Psychic?
However I do find it likely that neither one will get an evolution or prevolution...but Sun and Moon exclusive baby primates could be neat...