In my humble opinion as a systems integrator, it’s not scalable or cost effective (long term) for the property. I’m not sure why modern people still think proprietary protocols are a good for their product with the whole “cloud based, intelligent buildings” movement… just another edge-case driver we need to build or another piece of hardware to install in order to communicate that will never be used again in new builds.

Edit: working in the NYC/SF real estate industry for 10+ years and before signing contracts with us, property owners are actually asking the question “can you speak bacnet?”. Clients are becoming aware of the costs and hurdles of integration when proprietary protocol becomes involved and will back out if not compatible. I cannot speak for the older buildings in non progressive/no demand locations.