Point merge is being developed in the UK too for LAMP (London Airspace Management Programme). The Gatwick model does allow for conventional holding, but at stacks further away from the airport, and at higher levels to allow the departures to also climb higher. I think the plan is to allow continuous climb to at least FL100. However, most "holding" is done in a linear fashion along pre-determined arcs closer to the airport, and then at the appropriate time to achieve the desired spacing, aircraft are cleared for an RNAV transition for the approach and fly themselves onto the ILS without much (radar) intervention from ATC.