Perhaps, one could look in the book "The Right and the Good" by R. Daniel Z. Feldman, Section 11 titled "One Strike and You Are Out: Hitting and Raising a Hand in Violence", p 159-168. Since you are asking only about threats, I am providing the relevant middle subsection.
The basic implication of the gemara about this is that a person who threatens another with violence is a Rasha, as we learn from Moshe Rabbeinu and Dasan and Aviram (see OP for source).
Some hold that this is not to be taken literally in halacha, but is rather meant to provide a stigma against people who do this, as a deterrent to actual violence (e.g. R Aharon Grossman, VDarashta VChakarta pp 120-122).
There is discussion about the reasons for the prohibition. R Chaim Kanevsky (cited in L'Reacha Kamocha vol 3 #43) holds that the prohibition is actually intending harm, and R David Ariav (ibid) questions if maybe it is due to the fear instilled by the threat i.e. ona'at devarim. The nafka mina is if the person threatened didn't know about it, then there's no sin.
There are some who declare that the issue is the degredation of civil relationships; it is animalistic to introduce physical violence to a conversation, and this is an independant prohibition (see Parach Mateh Aharon, Mada, p.6).
If we hold that such a person is a Rasha, then they will be disqualified for testimony, especially if it is the latter reasoning that we adopt. The Rama rules that someone who does this is allowed to be a witness d'oraisa, it is nonetheless a rabbinic prohibition (some disagree, e.g. R Shlomo of Lublin, quoting R Moshe Mintz, Responsa Maharah MiLublin 89).
R Yehoshua Falk, in Sefer Me'irat Einayim cites the Mordechai that although it is a biblical prohibition, there are no lashes. R Shmuel Rozovsky (Chiddushei R Shmuel on Sanhedrin 12) holds that it is not d'oraisa, and the status of Rasha is not literal (the pasuk is just an asmachta).
R Yoel Sirkes on the Tur (Bayit Chadash, Choshen Mishpat 34) cites the Rambam and holds that it is indeed d'oraisa, and R Yehoshua DiTrani also holds this way (Responsa Maharit Even HaEzer 43 - note the objection of R Yosef Shaul Nathanson, Responsa Shoel Umeishiv, Mahadura Tinyana 2:70), and R Yaacov Veil takes this further and says there is indeed lashes (Responsa Mahari Veil 28).
R Menachem Mendel uses the later to question if a shochet should be removed from his position if he does this (Responsa Tzemach Tzedek CM Shaar Hamiluim 15). R Yehudah HaChasid states that the ban of excommunication that applies to actually hitting someone also applies to someone who raises his hand to do so (See SA CM 420:2, and Sefer MeIrat Einayim 4).
