I genuinely don't see Blizzard pulling a Demon Hunter and limiting a Tinker class (or whatever they'd choose to call it) to only a small number of races.
From a marketing/business standpoint limiting a class to some of the least popular races in the game is a serious gamble because while it could make those races more appealing it could also have the opposite effect and make the class less appealing, for Demon Hunters it worked because Night Elves and Blood Elves are 2nd and 1st in terms of popularity among their respective factions, asking someone to make a night/blood elf demon hunter isn't something most of the playerbase would be object to but asking someone to make a Gnome/Goblin Tinker? yeah i'm sure there are plenty of people who would object, Blizzard just isn't going to design a class to appeal to the absurdly small portion of the fanbase that actually likes Gnomes and Goblins.
From a story/in universe standpoint theres no reason such a class would be so limited, Demon Hunters from a story standpoint come from Illidans outworld forces and only Night elves and Blood elves were shown to be either in training or having become demon hunters from a lore/story standpoint such a limitiation made sense, meanwhile Gnomes and Goblins aren't protective of their technology at all, we've seen them train others in it's use, we've seen Dwarves, Orcs, Draenei, Blood Elves, Nightborne and Humans and more make use of technology either of their own design (Warframes, arcane constructs, blood golems, steam tanks, Dwarven Golems, Harvest Golems) or repurposed/designed from gnome/goblin technology (True/Iron Horde).
At the least i can see such a class being playable by Goblins, Gnomes, Mechagnomes, Orcs, Mag'har, Dwarves and Dark irons, Forsaken if alchemy gets incorperated into the concept, at the most i can see everyone but Night Elves, Trolls, Zandalari, Tauren, Worgen, Highmountain and Pandaren getting it since i don't think a technology class really works with those races respective themes/identity.
What is the actual important part of the blademaster as a concept? the illusion stuff or the mastery of the blade part?
What is the blademaster as a concept/identity? aesthetics and conceptually they are obviously based on the idea of a kensai/sword saint, from their japanese/samurai aesthetic to their abilities, If we go by the "weapons master/sword-saint" archetype thats covered by arms warrior while warriors don't have windwalk or mirror images i have to ask, what purpose does windwalk serve to the concept? what purpose does mirror images? these are the questions that need to be asked because in WoW a class is 20+ abilties, at least 2 specs and it needs to fit into the dps/tank/healer dynamic. the blademaster in WC3 was a duelist/hero killer, his abilities made sense for this purpose, windwalk let him position himself, mirror images gave him an advantage in 1 one 1, bladestorm gave him spell immunity, critical strike let him out damage other heroes, but in WoW this concept doesn't work we don't have hero killers/duelists we have damage dealers, healers and tanks.
Conceptually the blademaster doesn't work because the sword-saint/weapon master identity already exists within the warrior class and gameplay wise doesn't work because what the Blademaster was in WC3/HoTS is a duelist/assassin/hero killer a concept which doesn't exist in WoW.
Not to mention we literally have Blademasters in orgrimmar who are Warrior Trainers
https://wow.gamepedia.com/Blademaster_Ronakada
Same way Shamans absorbed the abilities of Farseers, Shamans, Witch Doctors, Shadow Hunters and Spirit Walkers, Warriors absorbed the abilities of Blademasters, Mountain Kings and Tauren Chieftains, Blademasters might be a unique concept in-universe but gameplay wise they exist within the warrior class