Bethesda are probably going to design TES and Fallout like this:
TES
TES DLC's
Fallout
Fallout DLC's
TES
TES DLC's
Fallout
Fallout DLC's
TES
TES DLC's
Fallout
Fallout DLC's
So don't worry, Fallout 4 will come after they're done milking TES.
As to New Vegas, it was
Obsidian who designed it, so you should thank them, not Bethesda.
And if you're expecting the same kind of greatness from New Vegas in Fallout 4 then you're likely going to be disappointed.