No it does not assume that. Some very smart people will write that model.toVHDL() function. And keep in mind that a DL model is only a very small subset of what you can use VHDL for, and most models will have a very similar implementation in hardware from a conceptual point of view.
And don't take it too literally, VHDL could be replaced by other hardware design languages, maybe even at lower abstraction levels.
Not trying to take it literally, but aren't there costs vs performance tradeoffs? Like the py.toHDL would have like (maxSize,maxCost,minThroughput) as free and that would determine energy usage?
And a GPU is already pretty optimized for inference, no? Like isn't it a bunch of FP mults? I don't think HDLs do well with that, either.