Okay, now for the remaining gods with no priesthoods. This is a very mixed bag of deities, many of whom are demigods.
Skiggaret – The Bugbear god of fear oddly has no priests. Since he is a demigod, he can only activate one avatar at a time, so I would expect he would embrace the use of priests to drive bugbears into fits of destruction. Some priests would probably re-interpret the god’s fear to being the fear they inflict on other races.
Stalker – This god, who is both part of all goblinoid pantheons and none, seems less likely to have a priesthood, but even so,a s a god of death, there would probably be a number of priests who would want to channel that against enemies. In addition, having priests would ensure the “Stalker’s share” of souls after battles; goblinoids might see the priests as some sort of protection from Stalker.
Zinzerina – This Drow demigoddess apparently wanders the Forgotten Realms (and has apparently been killed by Lolth, according to Demihuman Deities). However, some DMs may want to increase her power and spread in their own campaign. I’m sure she’d eventually have a priesthood were that the case.
Diirinka – I wasn’t sure initially if he should have a priesthood, but after looking up the Derro savants, I realized they would work pretty well as a specialty priest class. I’ll see if it is worthwhile adapting them to the specialty priest format.
Diinkarazan – Being absolutely insane, it seems unlikely that Diinkarazan would have a priesthood or grant spells. He might be revered by Derro intent on slaughtering Illithids, though.
Ilsensine – Maanzecorian has a priesthood, but he is a more concrete physical being, whereas Ilsensine is almost like divine mental energy. I’m not sure if it would be appropriate if both Illithid gods had priesthoods.
Gzemnid – Being a renegade from the Great Mother, it seems appropriate if Gzemnid is revered by Beholders who have broken away from the regular clans, such as Beholder Mages. He might even have a caste of renegade Beholder Priests.
Diancastra – This Giant goddess is really deserving of a priesthood, I think. She’d probably be a patron of a number of the lesser giant races (giant-kin), particularly firbolg and voadkyn.
Baphomet – This god, despite being a lesser god, is extremely restricted in his interactions, so I imagine the same constraints would prevent him from granting spells. It might be interesting to see what a priesthood would be like if those constraints were lifted, though.
Kostchtchie – This god of Frost Giants, and interloper on Thrym’s domain, has the ability to grant some powers, allowing for the existence of the “wyrmkin,” so a full priesthood is probably not far off.
Parrafaire & Shekinester – I am sadly not well informed on the habits and natures of the naga. I’ll have to read up on them before deciding if priesthoods fit their character. However, Shekinester would make for a *really* complex priesthood if it turns out they seem likely to have priests. However, after researching nagas, I discovered Guardian, Spirit, and Water Nagas all can cast Priest spells, so it may be appropriate to create priest classes for them.