I have seen a similar scheme on some older poles around here, although I'm pretty sure they are not isolated. If multiple transformers are running on the same primary, and their secondaries run to a common bus, the load should be evenly distributed, shouldn't it?
Newer installations are all triplex, and the newest services I've seen are completely insulated with plastic (no more ceramic) hangars. They look pretty weird, as the phases and grounding conductor can't be spaced more than 12" from each other, all using the same hangar.
The transformer that supplies my house is a 25KVA, and currently has 9 service drops running from it. Most of them are probably 100A, but that's still quite a stretch.
