The use of digital identities for internet users has been discussed in many places. And plenty solutions have been developed. There are lots of identity providers that offer (open) standards based digital identities that can be reused.
For companies the use of digital identities is only part of the problem, the use of external identities is just becoming a necessity.
Apart from offering access for external identities, organisations also have to cope with the internal identities of their customers. The more (legacy) backoffice systems organisations use, the more difficulty they have in identifying the value of their customers.
Nothing new here: this problem is solved in Customer Relation Management (CRM) and Master Data Management (MDM): we create a 'Golden Record', a unique internal representation of a customer, that is related to all coupled internal backend systems.
Master Data Management is an area with specific problems. How do you connect customer accounts in different backend systems with different identifiers. Backend1 customer A1 can be the same as Backend2 customer R2D2 and may not at all be Backend3 customer A1, but ASDFG9 instead. Master Data Management uses intelligent rules engines to connect Id's and knows some trics, like deduplication. I will not go into detail (I don't know this kind of process well enough).
In a sense both identity related problems look alike, although they are mirrored. Let me show it in a simple picture and await your reactions...: