I think these are too far (more in the 4h one way range)
I've added the others.

Wittenberg (Luther), Wörlitz and Dessau (Bauhaus) are easy to reach from the Harz.

On the other hand Quedlinburg and Goslar are easily reachable from Saxony Anhalt (let's say Dessau as a centre), so I would add them there.

Dubrovnik made it. :D You should add the Venetian Fortifications.

What about Kopenhagen?

Peloponnese Hotspot
I notice that this hasn't been assigned a "centre".
Tripoli is the geographic "centre" of the Peloponnese and all of the current connected sites are arrayed around it and is therefore the most obvious
However there are other WHS which are within a day return of either Tripoli or another location. I had started by looking to see which WHS had been connected to an "Athens" Hot spot - only of course to discover that there isn't one!!
We visited Bassae from Athens and returned easily in the same day by rent-a-car. Someone using Tripoli as a centre could easily get into Athens and back by car - and could pick up the Monastery of Daphni as well (as we did on our trip out to Bassae). They could even drive up to Delphi (via Hosias Lukas) and back - but a better "centre" would then be Corinth.
So there are potentially 3 extra WHS for a hotspot connection somewhere around Corinth/Tripoli - Parthenon, Monasteries of Daphni etc and , at a push - Delphi

I've added the center + the 3 extra WHS

Medina Azahara is missing from the Andalusia hotspot.

Adiyaman became a hotspot after inscription of Arslantepe.

1) Nemrut Dag (within Adiyaman province)
2) Diyarbakir (3 hour bus drive)
3) Sanliurfa (Gobeklitepe) (1.5 hour bus drive)
4) Malatya (2 hour bus drive)

You can check the bus schedule from this website - https://www.obilet.com
However, large buses are not the most convenient transportation route between Adiyaman, Sanliurfa, Malatya and Diyarbakir. There are minibuses that departs hourly till midnight from each city to the other. I do not know whether any English language information in the internet but they are quite easy to find. You need to go the main bus station (Turkish: Adiyaman Otogarı). https://goo.gl/maps/vY9652Qm6K6nGKSG9
Then you can easily learn the schedule there. There are more than 10 daily return trips to Sanliurfa and Malatya, and a few to Diyarbakir.

These are the minibuses:
https://www.google.com/maps/place/Adiyaman+bus+station/@37.7725,38.3225,3a,75y,90t/data=!3m8!1e2!3m6!1sAF1QipMA073BltPKiEiUPc7idXBA5Nqr0Il1yEoAsOJo!2e10!3e12!6shttps:%2F%2Flh5.googleusercontent.com%2Fp%2FAF1QipMA073BltPKiEiUPc7idXBA5Nqr0Il1yEoAsOJo%3Dw203-h152-k-no!7i4128!8i3096!4m5!3m4!1s0x1533137b8ab4f00d:0x58da678bbb5525d7!8m2!3d37.7721748!4d38.322731

Divrigi (we did Divrigi + Kemaliye as a day trip from Adiyaman (4 hours with private car), but I believe this does not count).

Edit: There are 31 daily minibuses to Malatya from Adiyaman. Here is the link (Turkish) https://hareketvakti.gen.tr/adiyaman-malatya-minibus-saatleri/
I am quite sure there are even more minibuses to Sanliurfa. I do not know the schedule for Diyarbakir but it is adequate to go there as a day trip.

Thanks! How shall we name it, the South Central Turkey hotspot? (with center Adiyaman)?