I learned with Bonsai that it is still whatever kind of tree, just smaller. We would never think about planting a Juniper, Japanese Black Pine, Maple or any other tree indoors. I think in terms of what the tree would require if it were grown as a normal tree.
Yes, heat and humidity requirements would be very helpful. I presume it took decades to collect the information for winter hardiness; I think collecting it for summer would be more challenging. Any nursery could collect the winter numbers, however the point of most nurseries is to get a plant to "growing size" and get it sold. They can collect info both of their own experience in survival as well as feedback of customers who lost a plant over winter. However the individual gardener would generally be the one who knows if it made it through summer. That info would be hard to discern though, since the group collecting the info would not know if the plant died from neglect, heat, humidity, too much rain/watering; there would be many unknown factors.
I can see where it would be difficult for nurseries to incorporate heat zone information. If I put a "full sun" plant in full sun and another in a less sunny site they would both be in the same zone; if the less sunny were morning or afternoon it could make a huge difference. The same is true of course for winter conditions - how close to a house, rocks, snow cover, windbreaks, etc. I guess when it comes to final analysis we try a plant and see what happens. Gardening is at more art than science. Finding others who are successful and asking questions is one of my most important tools - I could never possibly know everything I want in a lifetime.
