Lions are not very demanding about their enclosures. They used to do well in the old-fashioned big cat houses in our older zoos (like the Lion House in London Zoo that was finally demolished in the 1970s). The Whipsnade house looked fine to me when I visited last time. I think the 'glass wall' barrier is the first I have seen in the UK, but you will see similar designs in our Gallery from zoos abroad. I suppose an obnoxious visitor could try to provoke the lions from the other side of the barrier, but I don't think the zoo staff or the other visitors would tolerate that for long.
Alan