It is not a simple thing, because companies will have to pay to host on European servers, expensive ones.
Aqara is working on a hub to support Alexa.
Google Assistant I do not know, but I think it is the next step, as Alexa is the expensive one, due to the cost associated with being hosted in AWS servers (Amazon Web Services).
Xiaomi is fragmented in many brands, which may operate in different directions.
This is both a strength and a weakness.