Aside from the main series and that MMO, there was also a series planned "The Elder Scrolls Adventures" to which Redguard belongs, and "An Elder Scrolls Legend" to which Battlespire belongs. Is there any interest in BGS or some other studio doing more such games?

TES Adventures - a game set in a smaller setting, more focused on story and, well... adventure.

An ES Legend - again, a game set in a somewhat smaller setting, but basically an open-world classic TES game, only on a smaller scale.

I think these would be a lot of fun. Imagine traveling to some of the regions and islands that are less likely to be featured in upcoming games. These could be small, or in some cases large, a fill the void between games. Want to visit Morrowind? "An Elder Scrolls Legend: Telvannis" or perhaps the Imperial City in its full glory? "The Elder Scrolls Adventures: Imperial".

This is not supposed to be regarding the next setting or anything, or even TES VI, just to see if there is an interesting in revisiting these games. Rumors of a Redguard remake for example may be just what could set the series off again.

I wouldn't object as long as some other developer made them. I don't want Bethesda spending time on them.

That is a good point. Re-using assets, improving on mechanics, revisiting provinces/locations. Such things could be done by other developers, like Obsidian for example. A good example for a smaller, but still "New Vegas" sized game could be eastern Morrowind, specifically Tel Vannis, Firewatch and Necrom. Lots of interesting locations to be explore, and if they stayed true to the lore of the place, it could be a fantastic addition to the series, making way for a "side-series" to the main series.

TES spin-offs made by other developers than BGS would be a dream come true. I have a whole lot of ideas: a party-based isometric RPG like Icewind Dale or Baldur's Gate, a dungeon crawler like Eye of the Beholder or Legend of Grimrock, the possibilities are basically endless. Unfortunately, it seems to me that ZeniMax is not that interested in making these low-budget spin-off titles that don't cater to a wider audience.