I think the idea of a slayer locked ironman is an interesting take on a restricted ironman account. Being allowed to only keep items which are acquired as drops from slayer monsters, or or other items generated from those monster drops is a really fun challenge when it comes to theory crafting. Certain items like bowls are not directly dropped by monsters, and instead have to be crafted from soft clay, which generally has to be processed from normal clay. This adds a layer of complexity to interacting with the world, and especially when doing quests. Lobster pots can actually be acquired from dagganoths underneath the lighthouse, which makes dragon slayer seem doable, although the wizard mind bomb is tricky, which is a good lead in to some of the rules and restrictions.
Getting the basics out of the way, ironmen cannot trade with other players or use the Grand Exchange, but restricting the use of shops also makes sense on a slayer only account. What defines a shop compared to a service in game is a little hazy. Is a hide tanner a shop? What about a kebab seller, or the brewing assistant in Keldagrim? The location of the line is a little arbitrary, but what is widely accepted is that services are allowed, but shops other than the slayer shops are not allowed. This puts dragon slayer back on the table, since players could theoretically brew the wizard mind bomb for the quest, although the actual process is much more involved to get to the end result. "But this sounds like a normal ironman account, with extra steps!" I hear you say. And to some degree it is, although the unique challenges which come from the restriction make the game more novel and exciting from my experience, getting to enjoy all sorts of underexplored content in the game like the swamp weed cave bugs drop, which can be used to make soda ash, which in turn can be used to make early game molten glass. Or going to low level slayer masters to get skeleton assignments to hunt down rare drops from skeletal barbarians. It really changes the whole game experience when a meta is not well established.
Speaking of which, the RS3 slayer only ironman challenge is actually pretty different from the OSRS experience, with the first obvious change being the mining and smithing rework, which removes smithed items from drop tables, which really changes the account progression by removing the reliance on fire giants for an early game rune scimitar. Instead one must be smithed by the player, which requires the player to process stone spirits into ore, then smith the ore into bars, and then the bars into weaponry. In contrast to OSRS, stone spirits encourage mining, which can be used to give the player access to later game melee armor and weaponry. Of course the magic and ranged combat styles are also covered, as a lot of slayer creatures drop hides or cloth, which can then be converted into ranged and magic equipment. Overall, the slayer locked account has a smoother path to itemization, although the first step in acquiring a weapon is still a challenge, since punching spiders is difficult and awards no drops. Allowing item spawns to be looted can make the very early game significantly easier, but that is up to player taste. I do think that an exception could be reasonably made concerning quest items, since they could really restrict account progression, although any item which can be acquired as a slayer drop really should be gotten through slayer first.
All in all, I think the challenge is weird and exciting, and this is barely scratching the surface of all the weird quirks this adds to the game experience.