For now, I would imagine the owner sets up his own service, sub-panel, etc. off his main panel. If he exceeds the max load for his unit, he will pop his unit’s main breaker.
The follow-on question I would have is - does the feed for the entire building add up to the total for the individual units? I.e. if the unit has a 100-amp panel, for now, the 50-amp comes off the unit’s 100A and the owner cannot exceed 100A total, charging or not. (The car would pull a 40A load, the code sying max 80% of breaker) For example, my house has a 50A circuit for the charger off a 100A main panel, and only once did I pop the main breaker (which is why I dialled charging back to 26A from 40A)
But you have 6 units? Is the total feed for the building rated as 600A, or is it built with the assumption that all 6 units will never be pulling 100A at the same time? (For example, add up all the breakers in my house, they total well over 100A. But I don’t plug a toaster in every outlet, so it’s a safe bet…)
The problem you - or future owners - will eventually run into is - do you want to have all 6 units do the same thing? Is there even room on the electrical room wall for 6 of the 50A sub-panels? How tidy will it look? And maybe while the first panel is going in consider this - my experience with electricians and telephone workers where I worked was - given a big open blank space, they will plunk a new panel or baord right in the middle, no regard for future needs and other equipment.
OTOH - if you get to the point where 3 or 4 others want chargers and want to install a load-balancing system with metering and charge-backs (as linked above), the first one or two who paid to install their own will balk at having to pay again their share of a group charger… I hear condo boards can be fun…