The first question seems to point for the tense called "future perfect", or "Futur II" in German. It is used very seldomly to express actions or processes that are known to be terminated at a future point.
The example with the cat would be "Ich werde eine Katze gewesen sein", although that doesn't make sense as a sentence. Other examples:
"Im Jahr 2133 wird man alle Lebewesen geklont haben."
-> In 2133, all species will have been cloned.
"In 3484 Jahren werden alle Fisch-Arten ausgestorben sein."
-> Within 3484 years, all fish will have become extinct.
The syntax of "Futur II" is also used to express vague assumptions:
"Er wird die Tür
schon geschlossen haben."
-> He surely locked the door.
Aber das Auto wird
doch wohl nicht gestohlen worden sein
-> But the car won't have been stolen, right?
highlighted parts are used in these examples to further strengthen the opinion/emotion of the speaker.