There actually was an attempt at an Islamist coup in 1975 (backed by Pakistan):
"The arrival of Afghan opposition militants in
Peshawar coincided with a period of diplomatic tension between Pakistan and Afghanistan, due to Daoud's revival of the
Pashtunistan issue.[
citation needed] Under the secret policy of the United States and Britain, and the patronage of Pakistani General
Naseerullah Babar, then governor of the
Khyber Pakhtunkhwa, and with the blessing of Prime Minister
Zulfikar Ali Bhutto, camps were set up to train Hekmatyar and other anti-Daoud Islamists.
[16] The Islamist movement had two main tendencies: the
Jamiat-e islami ("Islamic society") led by
Burhanuddin Rabbani, that advocated a
gradualist strategy to gain power, through infiltration of society and the state apparatus. Rabbani advocated for the "building of a widely based movement that would create popular support".
[17] The other movement, called
Hezb-i Islami ("Islamic Party"), was led by Hekmatyar, who favored a radical approach in the form of violent armed conflict. Pakistani support largely went to Hekmatyar's group, who, in October 1975, undertook to instigate an uprising against the government. Without popular support, the rebellion ended in complete failure, and hundreds of militants were arrested.
[18]
Hekmatyar's
Hezb-e-Islami was formed as an elitist
avant-garde based on a strictly disciplined
Islamist ideology within a homogeneous organization that
Olivier Roy described as "
Leninist", and employed the rhetoric of the
Iranian Revolution.
[19] It had its operational base in the Nasir Bagh, Worsak and Shamshatoo refugee camps in Pakistan. In these camps, Hezb-i Islami formed a social and political network and operated everything from schools to prisons, with the support of the Pakistani government and their
Inter-Services Intelligence (ISI).
[20][21] From 1976–1977 Afghan President Daoud made overtures to Pakistan which led to reconciliation with Pakistani leader Bhutto.
[17] Bhutto's support to Hekmatyar, however, continued and when Bhutto was removed from power in Pakistan by
Zia-ul-Haq in 1977, Zia continued supporting Hekmatyar.
[22]"
https://en.wikipedia.org/wiki/Gulbuddin_Hekmatyar
Despite Pakistani support, the Islamists do not seem likely to me to prevail because (1) they don't have the base in the military that the PDPA (Communists) had, and (2) Daoud's regime unlike the Communist one that followed it, had not done anything terribly upsetting to most Afghan Muslims.