I can see what you are getting at, but lets look at this from the perspective of data-protection, a 3 node VSAN can only utilize Mirroring as its data-protection method, 4 nodes are greater is required for erasure coding. this mean a guaranteed loss of resiliency on loss of a site. effectively 3 single points of failure in your design.
this may be acceptable for a test and development environment, but never above.
I would consider separate VSAN nodes on each site and use VDP to manage off-site replicas. rather than run a high risk of such data loss.
This should be possible however there may be a license limitation if using Essential Plus.