Biden/Beto ticket wins Texas. Demoralizes the Republican party for a generation.
I think you're extrapolating too much from a very popular guy versus a really unpopular guy and a high minority turnout in a midterm. Dems are not winning Texas in a presidential year yet. Early polls are nonsense.
Biden and Beto cannot be the ticket anyway. Dems have to put a woman on the ticket. I'll say this. The final six are obviously: Beto, Biden, Bernie, Warren, Harris and Booker. No one in recent history has won the nomination when they're outside of the top 4 or 5 at this point in the process. Based on polling, one of those 6 is your nominee. Anyone below that is out of here and is simply angling for a cabinet positon. You saw that with Castro throwing shots at Sanders. That was an audition. I think if Bernie wins he takes a black or latina woman as his VP. If Warren wins then she takes someone like Beto. If Harris wins, she gets a white dude. If Booker wins then he takes a white woman and so on. If Biden wins then Kamala Harris is almost certainly his VP.
FYI, Beto hurts Biden more than he hurts anyone else. Most polls show that his entrance doesn't effect the Sanders/Warren wing. It has a greater effect on those more center types who want a new face. The way this lines up right now is that at some point Bernie or Warren will drop out and endorse the other one and consolidate the youth and progressive vote. Harris/Biden/Booker/Beto are all basically fighting for the same people. Based on that, one of Warren or Sanders is probably going to be 1st or 2nd in all of the early primaries. The lack of a young alternative to Bernie helps him (I don't think Pete has any shot...America is not electing a gay dude yet).
From where I'm sitting, the center had its shot at Trump in 2016 and the progressives will get their shot in 2020 with Warren or Bernie at the top of the ticket.