Ubisoft and Bethesda have their own unique style for producing and developing platform titles; a cross between the two could ultimately warp the experience of the next "GREATEST GAME EVAH!!!" rather than enhancing it.
However, that is not to say that certain elements that have been incorporated in past titles developed and produced by Ubisoft would not be welcomed by fans. For example, there exists Assassin's Creed 1 and 2. Specific elements, such as the core free-running mechanic were innovative ideas when combined with the graphical illustriousness of the titles, and could definitely have a place for an individual attempting to play a stealth-character type for, say, the next TES installment (which I will be referring to from this point on). Combat also had a unique place in both Ubisoft titles, with the stylized combat portraying a sense of legitimate competence on the protagonist's part, while allowing for creativity and development in the field. Would a speed-kill system be welcomed for the next installment? Sure, maybe. Also, high and low profile actions are a brilliant way to increase character immersion by generating a realistic crowd-response system; the idea is that individual NPCs or crowds of the characters would draw realistic individual/group response reactions to socially unacceptable or impressive behavior. An individual attempting a feat outside local or national law or of known infamy would not want to call attention to themselves, as that has the potential to draw the attention of law enforcement or the attention of authority figures, who would surely spell trouble for the individual. Lastly, in both Assassin's Creed titles, whenever a piece of equipment was acquired, it would become an observable item that was fitted onto the character in-game. Daggers, pouches, swords, maces, armor, and even other items could be easily identifiable when the character was examined thoroughly.
However, with those postulations stated, these elements cannot simply be ripped directly from Ubisoft's titles, due to complications that would arise from the gameplay mechanics. The core of gameplay developed in TES titles III and IV had a very specific feel, specifically founded on the precepts of character development, and exploration, the main focus of the game revolving around these two essential elements. If the elements drawn from the Assassin's Creed titles were directly pulled directly from the titles and transplanted into the next TES installment, there would all of a sudden be this tremendous shift in gameplay, because both said elements were the key focus of gameplay for both the Assassin's Creed titles. The focus of gameplay for the Assassin's Creed titles revolved around the characters' ability to go anywhere and strike from any point, and high and low profile actions that would allow characters to either blend in with their surroundings, or blatantly call attention to themselves, relating to the acquisition of intel relating to the target of interest, the actual assassination of the target, and the evasion that would follow.
Rather, Bethesda would need to alter these elements so that they serve to the original and true intent of the TES franchise, and not ultimately have it be the other way around.
Anyway, that's my two cents. Also, please forgive the next TES installment rant, but I figured it a perfectly logical hypothetical for the given situation.