Two weeks ago they did confirm this. It must be concrete because both are scheduled for 2021 and we have seen the first ADL leaks in the wild. Ponte Vecchio is a safe bet for TSMC.
IMO dual sourcing Sapphire Rapids makes a lot of sense. The most from the entire Intel lineup of 2021.
It's not even so much whether they can deliver a good product on 10nm (Based on Tiger-Lake they probably can) but whether they can produce enough without sacrificing any other 10nm products. Intel has undelivered to server OEMs for multiple years now and
trust is beginning to erode. If Ice-Lake SP is half as bad as Charlie claims (remains to be seen) then delivering Sapphire Rapid on time and in-mass becomes beyond critical.
Sapphire Rapid should have competitive core count to Rome/Milan (according to Charlie yet again), it also has DDR5, PCIe 5, newer Matrix/AI instructions and more. If Intel could deliver it in quantity in 2H2021 then they would finally have a product that has a clear edge on the competition at that point in time
Things wouldn't be nearly as rosy if:
a) It's postponed 6 months (as is almost a tradition @ Intel now) putting it against Genoa in 2022
b) They can only produce limited amounts of it (say 20% of the entire server demand). Be it due to yields, the need to produce all other kinds of (client) 10nm products or even unexpected demand.
Dual-sourcing would allow them to ramp up much quicker (and in larger quantities) and sell more Sapphire Rapids vs Ice Lake SP or god-forbid 14nm stuff and give them a safety net just in case 10nm "strikes again".
If I were In charge of delivering Sapphire Rapid on time and in mass, I'd surely have dual sourced it from both TSMC 6nm and Intel 10nm even if everybody underneath me in the organization would swear to god that: "In 2021 10nm will ramp up perfectly with godly parametric yields". Just on precedent of the previous years alone.
If the miracle indeed happens and 10nm really turns out so good that Intel can satisfy the demand
of the entire server market with only 10nm Sapphire Rapids (without losing out on any desktop/laptop sales) they could just keep the amount of wafers they order from TSMC to the minimum (rumored TSMC lead time of 6 months is plenty to call it). It would just be a good "proof of concept" for engineering teams. And sure enough engineers would learn a ton about making dual-sourceable designs, should the need resurface again a later date, say for 7nm CPUs.
Because of the forementioned stuff dual sourcing Sapphire Rapid looks like a total no-brainer. Particularity if this is now communicated on the top level ("we'll outsource where/when it makes sense").
Then again I'm a software-engineer not an MBA