The proposed connections below I've marked 'OUT' or 'IN DOUBT' – which means I will not add them to the website right now because I think they do not meet the criteria. Of course you can get them back IN – if I've misunderstood your hidden meaning, or if you provide satisfying arguments or if somebody else comes to your rescue when he thinks the connection is a good idea.
1. Canterbury can be added to the London hotspot.
OUT: it's either Canterbury or Stonehenge/Bath – all won't fit within a 250 km radius
2. Canterbury, Devon & Dorset coastline, Belfries [Calais & Dunkerque])
OUT: I don't really understand what is meant, please clarify (and there have to be 4 for a hotspot)
3. Famous architects: Acropolis – Phideas, Vatican – Bernini, Vicenza – Palladio, Milan: Last Supper – Bramante, Gaudi etc.
OUT: not specific enough, Palladio already has its own connection and so can have other architects (if they have 4 buildings in inscribed areas)
4. Scotland: New Lanark, Orkney, Edinborough, St Klida
OUT: this isn't a hotspot (the islands are too far for that), and I think it's a too obvious connection for pointing out a region
5. Volcanoes: Aeolian Islands, Pompeii, Jeju, Kamchatka, Dominica
OUT: we already have a volcanic category & a connection covered by volcanic ash
6. ARMENIAN ARCHITECTURAL STYLE: Haghpat and Sanahin - Echmiatsin and Zvarnots – Geghard
OUT: too obvious (it's a subdivision of a category & spans only sites in one country) (still a little in doubt though as there are Armenian monuments in other countries that could become a WHS)
7. Frescoes / murals by famous painters: Florence
OUT: this is too generic, especially for this connection specify which fresco or building, which painter
8. Tunisia and Low countries Hotspots
Both Tunisia and the Low Countries (Netherlands, Belgium and surroundings) have loads of WHS within a small area (small enough to meet the criteria).
DOUBT: they are not regions but countries, and the high density is 'just' a result of their being ultra-small countries; as this hotspot connection originated from its practicality for travel purposes, these should be IN