There is a difference in the upkeep of properties of the State by the Rijksgebouwendienst (State Housing Agency) and the exploitation of Het Loo as a venue which has to provide as much revenues as possibl to keep the estate running.
Seeing the flood of new ministerial departments, police offices, armed forces complexes, palaces of Justice, the renovation of state monuments (including the royal residences, the Rijksmuseum, the whole Houses of Parliament in The Hague, the Raad van State, etc.) there seems sufficient budget for renovations or to build new buildings.
The maintenance, the staffing, the utilities, the preservation of historical collections, the extremely elaborate (and labour intensive) 17th C formal gardens, it simply swallows money. That will be the reason for the need to have volunteers aside the paid staff.
Maybe the State, Het Loo and the Royal House (the most important "deliverer" of collections via their foundations) thought that this enlargement is necessary to generate enough revenue to keep Het Loo in spic and span state.
They have promised that the 17th C feel of the palace would remain unchanged. The only visible change seems to be glass panels on the front courtyard around the fountain, becoming the ceiling of the enlargement below but luckily no glass pyramid like at the Louvre in Paris.
The extension plan also brings some sadness: this means that definitely Het Loo Palace will never be a royal residence anymore. Of course it still will remain venue for events but with such an extensive underground lay-out like museum galleries, a foyer, restaurant, depôts and offices it will defenitely remain a palace with a museal destination.
Under Queen Juliana, Soestdijk Palace became the main royal residence and the The Hague office of the Queen was Lange Voorhout House. Noordeinde Palace even -partly- became a school... (Institute for Social History), was used as a royal depôt, housed courtiers. Huis ten Bosch Palace was largely out of the picture.
Under Queen Beatrix Noordeinde Palace and Huis ten Bosch Palace got a major restoration. As did happen to the Royal Palace in Amsterdam and now -again- to Noordeinde Palace. This means that after decades of "neglect" these residences could become in royal usage again.
The same did count for Het Loo Palace. It was restored in sparkling state but mainly remained a royal residence with a museal destination. Yes, on the terrain there are public services, an admission desk, a ticket office, a souvenir shop, but it remains a palace. With this major and costly underground extension, Het Loo changes from a royal residence with a museal destination into an outright museum. Period. With such major works it is hard go see that -for an example- the Danish example could be followed and that the King will use all his residences for a period of the year. Het Loo included. The Danish example guarantees that all residences, think at Graasten, at Marselisborg, etc. remain "living" royal palaces.
I am condident that the State Buildings Agency, the State Monuments Agency, the Crown Domains, the Palace Het Loo, the Royal House, the House foundations which give their collections in usufruct, all together will be very careful to keep Het Loo a fabulous palace indeed, but it is clear that we can forget ever a Queen Catharina-Amalia taking residence there for summer months. After all, until the 1980's the palace still served as a residence to Princess Margriet and her family.
I like the intensive and continuous care of the Dutch for their patrimonium, but this enlargement sadly also means the definitive end of any possibility to become a regular royal venue again, as -luckily- happened to the two palaces in The Hague under Queen Beatrix.
