Answering with respect to the Nestorians/Assyrian church of the East rather than the Jacobites (Miaphysites):
While not exactly a modern text, the Marganitha (13th Century) is a Assyrian (a.k.a. Nestorian) systematic theology in good esteem. There is a fairly readable 19th century translation into English in the public domain provided on wikisource.
Unfortunately, I doubt there would be any more modern examples, especially given the history of the Assyrian church. Before the 20th century, there would be little motivation to write a systematic theology in the English language. During the 1920s, they suffered a genocide under the Ottomans (The so-called Seyfo), and the subsequent emigrations meant that the immediate pastoral concerns of reorganizing a previously geographically isolated church on a global scale (in foreign cultures no less) were of more importance than writing systematic theology. Likewise, recent ecumenical efforts, which by their nature tend to involve looking back at historical theological positions rather than creating new works, may account for the lack of such a systematic theology.
A Modern (2006) Assyrian Catechism (rather than systematic theology) can be found here by C. Klutz and G. Toma. It has a Bibliography which includes the above-mentioned Marganitha, as well as a number of other volumes, which may be of interest, though they do not all appear to be in English.