I am not sure what you really want, nor for that matter, it you know what you really want. I think somebody already asked you but I didn't see what I thought was in informed answer, so it is difficult to give an answer. Confused?
BJJ, Judo and Hapkido all have different philosophies in how they react to an attack. You need to find out what those are, preferably from schools in your area if they exist. What little I know about BJJ and Judo, they have no problem making contact while both are on their feet. But the preferred goal seems to be to get an opponent to the ground and apply some technique for a pin or submission. That is OK if that is what you are looking for to complement your TKD. But as others have stated, I personally would prefer not to be on the ground. From the little I know if either, I think Judo is a little more willing to perform a throw staying on their feet, and walk away if the opponent has the common sense to allow that to be the end of the confrontation. BJJ and Judo practitioners are welcome to correct me because as I said, I don't really know those arts.
There are a lot of flavors of Hapkido. Besides that, Kuk Sool Won has a lot of defenses that are shared between them and Hapkido. But I think most, and certainly the Hapkido I studied, are all very defense minded. We normally wait for and respond to an attack. Many strike and kick defenses will start with a block/evasion, then a grapple, often dislocating a joint, and finishing with the opponent on the ground receiving a strike or kick. Even if an opponent starts with a grapple, we will have a defense that may often result in the opponent being on the ground (not us other than kneeling), and receiving a kick or strike. Those are very common things. That said, we do teach recovery from being taken to the ground, but it is usually at higher belts so you can more easily pull them off based on your prior knowledge.
That is why I would also think if a person is looking for an add-on to TKD or even Karate, Hapkido is a good supplement. But if BJJ or Judo can honestly say they tend to use their grappling to get to a strike or kick, then they might be OK as well. But again, I don't think that is their main thrust. Regardless, if you have gone to Hapkido, BJJ and Judo schools, and prefer one over the other two, do the one you prefer.