Let's consider (and extend) the notion of cases for nouns located somewhere, and nouns heading somewhere. I.e. this wouldn't be "the man is at the lake", this would be "the man who ats is (at, with regards to) the lake" or some other silly way of expressing it. Let's consider how this interacts with
- subjects vs. objects and alignment more generally
- more metaphorical uses (e.g. becoming, being, being averb, going to verb)
- indirect objects and such
- more general effects throughout the language
Ok, so we come up with two cases, the stationary case and the motionary case. The stationary case is used when we state that the subject (or object) is located somewhere, or that the object is located somewhere as a result of a static VP: e.g.
A holds B.stat (in place)
A encloses B.stat
A contains B.stat
The motionary case is used whenever motion is involved, obviously:
A.mot approaches B
A.mot leaves B
but also when A sets B in motion:
A scared B.mot (away)
A threw B.mot
A pushed B.mot
Verbs like 'leave' and 'come' may not be distinguished, and are not strictly speaking morphologically distinguished either: both involve a motionary subject, and both involve motion (obviously). Adverbs may serve to indicate the direction, but also context. As far as cases go, this seems to behave entirely unlikely both subject and object marking, and one would expect there to be some kind of object marking (or ergative marking) to balance this system up, so that the non-motionary non-stationary argument's role can be unambiguously parsed. However, it's not entirely unconceivable that each verb's semantics is clear enough that no subject/object distinction is needed: the motionary/stationary and the unmarked noun may well have easily parsed roles.
As for more metaphorical uses, we can consider the way many languages use locative expressions with infinitives, similar to how the 'to' in 'to VERB' became part of the infinitive construction in English. At this point we can consider the regular locative as 'being averbing', and the lative as 'going averbing'. In this case, a subject that is averbing would be stationary, and one that is going averbing would be motionary. However, in causative utterances (or utterances of, say, seeing someone verbing) the causee (or the object) could easily be in the stationary, or motionary, depending on the aspect and tense and whatnot of the situation.