But unfortunately, I don't think there'll be TES6. We here are all mature Morrowind players, so I think it is safe to discuss this without instigating drama.
It's just not feasible for Bethesda/Zenimax to start TES6 while ES Online is going (remember Warcraft). And due to nature of MMOs such project may continue forever.
I base this assumption also on declarations from Bethesda that "don't expect a new TES game in a long time" and "we'd like to develop a new IP (intellectual property, meaning another game aside from Fallout and TES series)"
There will be another TES game, Bethesda made that very clear by saying TES 6 will be delayed in favor of Fallout 4
I think this one is a valid proof (if they said exactly this sentence, they probably planned TES6 after all), but can't agree on your other points.
TES is successful, but ESO is a part of the series (absence of number "6" means nothing), just MMO. And Bethesda is a part of Zenimax, and they are physically located in the same building. Speaking of canon, I don't think they really care about such things on management level.
Anyway, I would love to see TES6 released, and I would be happy if my prediction proves wrong. Also note that I am not an "ESO hater". I think it's a solid game, according to what people say.
I've never really understood the argument for why we can't have both ESO and TESVI. The two are clearly very different games with different audiences that appeal mostly to different people, developed by different studios with different teams in different towns (Bethesda Game Studios is in Rockville, Maryland while Zenimax Online Studios is in Hunt Valley, Maryland), with very different margins of success (Skyrim sold well over 24 million copies, while official data for ESO suggests it has yet to hit 5 million sold copies).
ESO can't really be compared to WoW either, since ESO was made by a different team at a different studio (as opposed to WoW), and because ESO doesn't have a subscription model anymore, almost all of the profits are coming from sales of boxed copies. Skyrim sold 7 million copies in the first 48 hours of release, while ESO, after a year, has again yet to hit 5 million. From a business standpoint, it makes little sense not to continue with the core series where any future releases will be met with financial success almost immediately.
Any delay in the release of TESVI will most likely have to do with Fallout 4 (which is developed by the same team) rather than ESO, I should think, since Bethesda does already have an established pattern going from Oblivion to Fallout 3 to Skyrim.
But anyway, that's my 2 cents on the matter.