I am of the opinion that the theme "repentance" is not given enough space in works on systematic theology.
Just look in the index for a paucity of references in a random modern systematics on your shelf, I challenge you.
Perhaps because it is associated with "pastoral theology", not systematics proper? Perhaps because it is seen as rather old-fashioned religious language? Perhaps because it has negative connotations associated with conditionality and contractual theological schemes? Perhaps because it seems too moralising?
All involve misunderstandings.
And it remains true that it was a central theme in the ministry of Jesus. A thesis: it is the misappropriation of the language of "repentance" that has lead to its neglect.
In the above picture, Thomas Söding (in Die Verkündigung Jesu) writes about the nature of repentance in Jesus' proclamation. The coming of the kingdom doesn't depend on repentance. It's the other way around: The necessity and possibility of the repentance and faith depends on the nearness of the kingdom.
This resonates somewhat with Calvin's distinction (in the Institutes) between "evangelical" and "legal" repentance.
"Others seeing that the term is used in Scripture in different senses, have set down two forms of repentance, and, in order to distinguish them, have called the one Legal repentance; or that by which the sinner, stung with a sense of his sin, and overwhelmed with fear of the divine anger, remains in that state of perturbation, unable to escape from it. The other they term Evangelical repentance; or that by which the sinner, though grievously downcast in himself, yet looks up and sees in Christ the cure of his wound, the solace of his terror; the haven of rest from his misery"