I largely agree with the quote you cited.
If temperate climate specimens are used and kept exclusively indoors, the will eventually weaken and die.
1. When they say "eventually", does it mean months? Years?
That's not the sort of thing that is easily quantified. If you kept, say a Maple, inside it might do well the first year provided you were able to meet it's basic requirements. But if you force it to remain 'green' during the winter it would likely fail sometime the following year.
Junipers that are sold this time of year face different problems. These young plants are re-potted inappropriately, shipped, mishandled by retailers, and sold to people who may not have any idea how to handle them. By the time they are in the hands of the recipient they have endured so much abuse that often it is too late. It is no wonder that that these 'Christmas Junipers' are almost doomed from the start.
Sometimes, people will keep indigenous species of deciduous bonsai trees in their refrigerator for a few months to Ã¢â‚¬ËœwinterÃ¢â‚¬â„¢ them.
2. What about the refrigerator solution? Is this feasible? What about light?
Although I have never tried this I have read of others who have. I think the key word here is deciduous
meaning that they have no leaves while dormant. No leaves, no need for light. I don't think I would attempt to keep an evergreen under those conditions.
"Indoor bonsai are trees cultivated and intended for indoor display only..."
I think this could use a little clarification. While it may be true that " 'indoor bonsai' are cultivated
for indoor display" that does not necessarily mean that they must
be kept indoors. These same species can be kept as outdoor trees provided your climate allows it. I keep everything I grow outside during the summer, moving tender species inside only as winter approaches.
I may take some heat for this but there really are no 'indoor trees' merely species that can adapt to a life indoors. Some species are inappropriate to keep indoors, some will do OK but not really thrive, others can do surprisingly well if managed correctly. This almost always means supplemental lighting and perhaps even a humidifier.
If you intend to pursue indoor bonsai you need to look to tropical or sub-tropical species.