Well uhm, while I don't understand why someone would want to support a faction whose members clearly lack subtlety and the ability to at least pretend to respect the other cultures so they might not be hated by all of Tamriel at the end of the day...
...I do understand when people get seduced by their awesome voices. Plus they're my favourite villains so far because they spawn and I can let my bad mood out as long as my computer still runs.
Therefore, I'll make the best of this post which was probably meant to be provocative?:
With the Thalmor being all like
And the Emperor accepting the WGC being all like
And the Talos lovers being all like
And Ulfric and his Stormcloaks clinging to their Talos-Amulets being all like
And the Jarl of Whiterun about Talos worship being all like
And then eventually, the Empire's Legion hopping into Aldmeri territory being all like
And Malborn at the Embassy being all like
'Cause the NPC dialogue shows that while Legion and Stormcloaks surely hate each other, a common foe will bring them together (both sides thought about making a truce to fight the dragons; feel free to look it up!). So even if Ulfric is killed, his Stormcloaks won't hesitate to join the Legion if it means bringing the Thalmor down right at their borders to Cyrodiil. And if Tullius is killed they'll be independent and stuff and Ulfric will be wanting a place next to the Legion when it comes to fighting them down faster then they'll be able to actually flee Skyrim (maybe one of Bethesda's artist folk could make an artwork with a few Thalmor hanging from the gallows, Elenwen specifically). Or maybe both endings we can play are not the Lore-ending, just opportunities to see how both things would run out if they ended like... well, like they do when you join one of the factions.
Purely theoretically of course. Who knows what Bethesda will come up with for TES6.