If they make a Switch that has no detachable joycons and its not made to dock in mind(Home console), you are severely limiting not only the Switch potential, because you are offering a worse product at the cost of little gain(The cut in costs of production would be really small), but you are potentially fracturing its own audience, due to games wither having necessity of the joycons being separated from the hardware itself, or just because of games that are played better on the TV rather than the small screen on the system.You could say that they could simply buy the acessories separetely, but then thats an extra cost, and its a hard pill for the consumer to swallow, given that they would feel that they are not getting the full experience.
No, it wouldn't fracture the audience. Normal joycons would of course stay 100% compatible and you can buy them later as accessories, if you want or need them for some games (and save that money if you don't want to play these few games with mandatory joycon input)
Just like Switch owners buy an optional Pro controller since Switch launch if they want it for some games. WIthout the Pro controller you don't get the full experience either. Without the Retro NES Joycons you don't get the full experience either.