Apparently researchers have measured this, and for people meeting in person it's normal to maintain eye contact 30%-60% of the time in a conversation [1] with each contact lasting ~3 seconds [2]

So a system that maintained eye contact continuously would indeed risk looking creepy!

[1] https://www.forbes.com/sites/carolkinseygoman/2014/08/21/fac... [2] https://www.businessinsider.com/heres-how-long-you-should-ho...