Bethesda didn't put nearly enough time in Morrowind and Oblivion then they did in Skyrim that's obvious to everyone. The proof traveling to the 4 provinces in Skyrim? Walk to the 4 corners of the map and you will find a gate to each leading specifically to that province, aside from that it is also in the coding and you will get to them off map with Console codes, PC players know this. Also in my last post i corrected myself saying it's highly doubtful their will be a TES VI so you're late posting. It all comes down to a matter of opinion, so don't call someone naive for that or you will put yourself in a Netches nest buddy ;D
The only thing in the coding is in regards to anything outside of Skyrim is in the 1.8 patch in regards to Dragonborn. There is nothing in the code in relation to Hammerfell, Cyrodil, or High Rock. The gates around Skyrim's map have no indication to do anything with future DLC, and their resceptive COC Locations all use the same default generic "Wilderness" cell name all exterior cells have on world creation, so there's no way to "get them off the map" with console codes as they're all unmarked locations. As for time, Skyrim had the
least development time of the past 3 Elder Scrolls game, of 3 years. Oblivion had a development time of 4 years, and Morrowind had a development time of 5 years.