On the PS4 and 720, would it be possible to fit in Hammerfell and Cyrodiil (as examples) to the same level and quality as Skyrim, or even better?

It would take twice as long to make or be half as detailed.

I've often thought that Bethsda would merge Elsweyr and Valenwood seeing as they're so small.

They better be super computers if so

I could live with that. I really want to see Valenwood:

Valenwood is a largely uninhabited forest wilderness. The coasts of Valenwood are dominated by mangrove swamps and tropical rain forests, while heavy rainfalls nurture the temperate inland rain forests. The http://elderscrolls.wikia.com/wiki/Bosmer live in clanhouses at sites scattered along the coast and through the interior, connected only by undeveloped foot trails. The few Imperial roads traverse vast dense woodlands, studded with tiny, widely separated settlements, and carry little trade or traffic of any kind^{http://elderscrolls.wikia.com/wiki/Valenwood#cite_note-0}. Furthermore, the nation is home to giant, migratory trees, such as http://elderscrolls.wikia.com/wiki/Falinesti, that house their cities.
Much of the region is impenetrable mangrove and coastal rain forest, with few grasslands or glade areas until further north near the http://elderscrolls.wikia.com/wiki/Strident_Coast?action=edit&redlink=1. It is "a sea of endless green, a maze of foliage with half-hidden cities growing like blooms from a flower", and "the home of the Bosmer is Tamriel's garden" ^{http://elderscrolls.wikia.com/wiki/Valenwood#cite_note-PGE3:V-1} http://elderscrolls.wikia.com/wiki/Domica_Redwort is a herb grown by many residents of Valenwood for their beautiful and showy flowers. They attain a height of about three feet and have feathery leaves; the flowers are usually bright red. In addition to their beauty, they are said to have magical abilities to enhance the appearance of anyone who carries or wears one of the flowers. ^{http://elderscrolls.wikia.com/wiki/Valenwood#cite_note-2}

Bigger isnt better

Yes, but it would be a god aweful representation of those provences.

Besides by fusing provinces your taking another potential game out of the TES seires.

You can't possibly think that a series as successful as this would just stop when they finish Tamriel. If they make money with it, it won't end.

In Tamriel, people jump just as high as on Earth. If we're to assume that the physics of Earth applies at least in part to Nirn, then Nirn is as large as Earth. Even the design of the largest Elder Scrolls game yet, Daggerfall, is only as large as Great Britain.

If my speculation proves true, there's a lot of room left for some Elder Scrolls mischief.

Size has never been a hardware issue (okay, maybe tangentially a storage space is an issue but Skyrim uses only 60-70% of a DVD). The issue has always been the amount of "content" and the variation thereof. All the dungeons, quests, etc don't take that much space and having more doesn't dramatically increase processing cost because only a small subset is loaded at any specific time. What is the problem is that it takes time and money to make all that stuff. Bethesda consider themselves to have a good size to content quantity/quality ratio and are unlikely to change.

Aside from ESO I only see Valenwood and Elsweyr or hammer fell and high rock being merged.

Tamriel isn't the only continent on Nirn, as shown on http://forums.nexusmods.com/index.php?/topic/70963-nirn-brandnew-full-map-created/

Possible? Yes.
A svcky idea? Yes.
Elsweyr deserves its own game.

To be fair, the beast races are in dire need of some TLC.. be it Elsweyr or Blackmarsh. Either way further entries into the series will be a win .

Changing continients.....idk what I think about that