Specialist seed: As far as I know these are not protected and growers can continue growing crops year after year and even continue cross breeding with other varieties. So the industry remains relatively small scale. This is not true for most GM crops where seed sterility methods can be used to ensure transgenic crops cannot be propagated.
Other advanced methods: Don't know, but expect that sometimes there have been disastrous consequences for some 3rd world producers, either leading to market collapse, hence fairtrade initiatives, or environmental disasters due to inappropriate use of fertilizers, pesticides or weedkillers, even change of land use.
The point is that as each new GMO has to be individually approved all predictable consequences should be taken into account and information can be made available so that consumers can make their own choices.