The model is as useful as the predictions. The factor by which the GDP is boosted based on tech stocks valuations is the random factor. Including tech speculation has distorted the published GDP. Granted, tech speculation is cause for increased velocity, without commensurate production.

Modeling that the GDP goes up because people are buying bitcoin would be the equivalent of the AI investment effect. A key difference being that the AI companies are currently included in the calculation and bitcoin is not. I don't mean to imply that the AI companies are transparently ponzi schemes, but they are all massively overvalued. The net GDP effect should be very very small if not negative, while the valuations are being used to justify a growing GDP that would otherwise have obviously fallen.