A weed is generally considered as being a wild plant out of place so what is considered a weed in one scenario may not be considered as a weed in another.
Given that there are a lot of varieties of wild plant out there, you may find it difficult to find enough reliable training data to be able to identify all weeds.
It can also be very difficult to distinguish between a wild plant and a cultivated plant at the early seedling stages but very easy at the flowering stages.
You may find it is easier to flip the problem around and identify the cultivated plants and treat the unrecognised wild plants as not a cultivated plant, as you are likely to have a lot less cultivated plants in a given space to identify than potential weeds.
It's also likely going to depend on how well you can control the environment.
