A friend of mine who builds trailers and sells them on (several makes), mentioned to me the other day that talk from his suppliers is that braked trailers and mots for all will follow. He dreads this as the cost implications will have an big impact on his future sales. That is buy a trailer now, pull it away, no more worries - job done! (Not withstanding wheel bearings). Add an MOT and braked mechanisms - worries, and therefore I won't bother. It won't happen overnight but at some stage it may be all trailers bought after xx/xx/xx must have........ etcetc.
Only time will tell!