My 2cents on OGS.
If someone is looking for the service (VPN in this case) load balancing located at the same location then OGS may not be the best option. The idea behind OGS is to measure latency (round trip time) per headend and then connect to lowest latency headend from client perspective.
So in true sense I wont consider OGS as load balancing unless user base is global and headends are also global.
Another solution that I have seen in the field is based on DNS, we can simply use DNS weighed round robin like AWS's Route53 to balance traffic between multiple headends:
https://docs.aws.amazon.com/Route53/latest/DeveloperGuide/routing-policy.html#routing-policy-weighted
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Weighted routing lets you associate multiple resources with a single domain name (example.com) or subdomain name (acme.example.com) and choose how much traffic is routed to each resource. This can be useful for a variety of purposes, including load balancing and testing new versions of software.
To configure weighted routing, you create records that have the same name and type for each of your resources. You assign each record a relative weight that corresponds with how much traffic you want to send to each resource. Amazon Route 53 sends traffic to a resource based on the weight that you assign to the record as a proportion of the total weight for all records in the group:
Formula for how much traffic is routed to a given resource:
weight for a specified record / sum of the weights for all records.
For example, if you want to send a tiny portion of your traffic to one resource and the rest to another resource, you might specify weights of 1 and 255. The resource with a weight of 1 gets 1/256th of the traffic (1/1+255), and the other resource gets 255/256ths (255/1+255). You can gradually change the balance by changing the weights. If you want to stop sending traffic to a resource, you can change the weight for that record to 0.
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One downside that I can think off is we may loose features like AnyConnect reconnect etc.
