In the tvtropes article on Youkai, the following remark is made on the meaning of "obake":
Obake is another Japanese word that can indicate some type of monster. Derived from the word for "to change", it generally covers the subset of youkai that includes shapeshifting animals (hence the terms bake-gitsune, bake-neko, etc.) as well as Animate Inanimate Objects 〔i.e. tsukumogami〕. Confusingly, however, the word obake can also be used to refer to ghosts, also known as yuurei.
The Wikipedia article on Yōkai contains the (unsourced) statement that
Yōkai that shapeshift are known as bakemono (化け物) or obake (お化け).
The Wikipedia article on Obake contains the (unsourced) statement that
Literally, the terms mean a thing that changes, referring to a state of transformation or shapeshifting.
The implication that the bakeru root of obake/bakemono is related to the ability to shapeshift is a strong one at least as far as public opinion on the internet goes, despite the inconsistencies that can be noted with this etymology. In my estimation, the less incongruous root of the term would be that it refers to beings that have undergone a change; they might also (coincidentally) have shape-shifting powers. Many (perhaps not all) of the shape-shifting animals, which are considered obake, are transformations that happen when an animal has lived for a considerable amount of time (commonly 100 years); the tsukumogami, being items, commonly attain their status by considerable age as well, in particular by having been abandoned or forgotten or not well kept. In the case of yurei, the transition is that from the living to the dead. While this etymology seems to capture all of the cases that fall under obake (shapeshifting animals, animated items, ghosts), it would also exclude some other yōkai that are shapeshifters, but have not undergone a transformation, such as most prominently the oni, which ought to fall under obake if we considered it to refer to shapeshifting.
Is my reading of obake as referring to "transformed entity", rather than to "shapeshifter", a sensible one? Is there any support for it? Any credible scholarly sources that contravene it?